@bevhills But it seems like you are concerned the parent won’t be around for the ceremony. Does everyone understand the seriousness if that is the fear?
If everyone knows the diagnosis, then what do you have to gain by saying something?
Forgive us, we all know you’re trying to do right by everyone in a situation simply isn’t good. But I honestly think it would be better not to say anything.
I’m not quite understanding the new information you’d be bringing to the couple. If you would be bringing private health information not known to the couple, and known to you only by chance, this seems to me to be an invasion of the patient’s privacy.
I wouldn’t intervene, but I might consider telling the in law that you saw her. I would want to know.
@bevhills You know the nice thing about the situation is that you have two families that care about each other and two young people are in a great situation. Waiting might not be a choice that I would make it I was worried about losing a parent. What you could do is simply ask how X has been doing?
With the extra facts, I might bring it up with my child that moving up the dates might be considered, just to get the couple thinking of it.
Actually it is the father who is ill. The mother died a few years ago in an accident.
Except this conversation is about the timing of the marriage, not whether to get married. And making a baby or two can be very relevant to the timing of a marriage.
Are you bothered that they aren’t married yet? Do you feel they should be more committed to make the final plunge?
@bevhills O’k I’m projecting but it was especially important for my father to be at the wedding because it meant so much to him. We’re kind of socially liberal traditionalists if that make any sense. I also know that there were times I was appreciative that someone reached out and helped me make a correct choice. The most important part of this is knowing your audience!!! If you think there is great concern for dad’s health and NOT having dad at the ceremony would forever bother the couple (because projecting it would always bother me if I could have shared this moment with dad that was so important to him and missed it). This is interfere-y but maybe…
How is dad doing?
We are so happy that you two are together and support whatever you’d like to choose. But it is a fear of mine that Mr. X might not be able to share this special day and I know it means the world to him.
That would be honest.
Do we Know if Mr. X feels like he doesn’t want to miss this wedding?
In my opinion that is a conversation for Mr. X to have with this couple…not anyone else.
It sounds like there is a lot on the family plate right now…and plannigneven a small wedding isn’t the highest priority,
Be supportive… but I honestly do not think this is your subject to being up.
My brother set a date for his wedding about a year in advance when he’d learned at least six months previously that our father’s cancer had progressed and only had a 50% chance of surviving for an additional 18 months.
Our father did not survive to attend the wedding - there was a remembrance candle placed in the location where he would have been sitting. I wondered why my brother didn’t select an earlier date, but never offered my opinion or suggested that he do that as I didn’t consider it my business.
I really don’t know if my father would have wanted things to be rushed for his benefit or not. When he was doing chemotherapy - he didn’t want any visitors (including me or my kids) because he just didn’t have the energy to deal with us and the side effects made him very ill. He loved my girls - he’d strike up conversations with strangers at the grocery store just so he could show off their photos. They were young at the time and very cute. But he absolutely did not want us around when he was feeling badly - even though we lived in another state and were only able to visit once or twice a year.
If the father is as ill as the OP thinks he is, participating in a wedding might be the last thing on his mind.
On the other hand, I think my brother was in denial about my father’s chances of surviving - as were we all. His death came much sooner than anyone expected*. I think he died about three months after my brother set the date, but he was active and still working up until two weeks before he died. I would hope the couple realizes that things can change very quickly for the worse and are taking that into account in their life choices.
*The same situation happened with my FIL. My husband and I visited him when he was ill with cancer and we could see that he had declined since our last visit but he was not bedridden and did not seem on the verge of death. So I sent an e-mail to my husband’s 7 siblings and told them about his condition - my main observation was that he was often short of breath. The eldest son advised everyone to not jump to conclusions and suggested that people visit in groups of 2 or three over the next few months. Their father died two weeks later - and none of them got the chance to see him again before he died. For both of our families, none of us seemed to understand how fragile the lives of our loved ones were.
@bevhills It really depends on the dynamic of your family also. Within my family, I would prefer straight forward expression of concerns. And then we can talk about it. It really depends upon your family’s accepted and expected personal spaces.
When my SisIL was ill with cancer, we got a call from a close family friend. He suggested we ought to visit sooner than later, as we had visited her many times previously and were trying to figure out the timing for our next trip to see her. I asked the friend about a weekend a month out and he said again that the sooner the better. We and our kids were all there that weekend—she died just as our plane touched down on our return to HNL.
It’s really tough to KNOW how long any of us has. I’d think if the ill person cared and wanted to express his desires he would have done so.
You should absolutely and totally stay out of it. When to get married is up to the engaged couple. Stay out of it.
Since the illness is known, is there anyway of inquiring how the father is feeling? Maybe this way they may be able to share exactly what they know.
“Hey not-yet-il, I ran into your dad last week at Dr. X’s office. We didn’t have time to chat, but it made me wonder how your dad is doing. And then I started thinking about how unpredictable life is, and that there is no reason to wait umpteen months to get engaged and umpteen more to get married unless you really want to do things that way. If you and my-kid want to move your dates up it’s more than fine with me. Just let me know where and when, and I’ll be there.”
^^ Just no. Stay out of it.
If you are close to the family, then perhaps you could actually call the Dad? Let him know you saw him at your oncology appointment, and simply ask how things are going? See if he’d like to “all get together for a holiday lunch” or something holiday’ish.
Any of us who have an oncologist understand that those appointments can be just follow ups, or something much more serious, or anything in between. We also know that things can turn quickly, and not ever return. I believe OP has heart in the right place. Life is precious, as we with oncologists know.
The young couple has been dating since they were 16 but how old are they now?
My dad has had leukemia for several years. It’s not curable but it’s treatable. He is enjoying life in retirement after having been a professor for 52 years. If this had been 30 years ago, he probably wouldn’t be around, but with today’s medicine, he has a good chance of being here to see all of his grandchildren grow up. 
I hope I’m in as good as shape when I’m 80!