I’m responding to the part that I bolded above. 
Amen. Totally. 100% agree.
I used to be the party planner & chief social get-together organizer with all of Husband’s extended family (MIL, his sister & her immediate family, his aunt & uncle). None of them could ever manage to make decisions on anything & everybody for YEARS would just look to me to play the role of chief cat herder & dysfunctional family project manager.
And for 25 years, I did that.
And then I got breast cancer. And had to take 3 months off of work to recuperate from 2 surgeries due to a double mastectomy. And guess what? Barely 2 weeks after that was all done, they all started asking, “What are we going to do for the holidays?”
So I told Husband all the rest of the crew that I didn’t have the energy or wherewithall that year to plan ANYTHING, that they all can figure it out and let me know what the plans are and we’ll be happy to participate and help out…but I am NOT going to be the party planner that year.
Toward the end of October, nobody had made any decisions and I was still getting phone calls weekly asking what are the plans for Thanksgiving and Christmas. It was like all of them had forgotten how to adult and make a decision.
So I told Husband that he had 2 more weeks to figure it out and then if there were no plans, I was going to make plans for our immediate family only since nobody else can actually talk to each other. 
The inevitable happened. Nobody made a decision. They were all waiting for me to come up with a plan. Well, I invited friends of ours over for Thanksgiving & my sister came, too. We had Thanksgiving in our pajamas that day and it was a wonderful day to be alive.
Those same friends invited us to their house for Christmas. So we spent 4 days at their home in southern CA over Christmas. That was an awesome Christmas. Introduced my kids to Die Hard and we’ve had debates every since on whether or not it’s a Christmas movie. LOL.
Meanwhile, Husband whined about “What am I supposed to say to my family?” I don’t know…how about the truth? The truth being that we made other plans because they couldn’t & wouldn’t propose anything, so we figured they weren’t interested in doing anything with us. And I told him that he could let his aunt & uncle know where we were w/our friends in southern CA (~1.5 hr drive from the aunt & uncle). Our friends said, “Sure! Have them join us on Xmas Eve or Xmas Day! It’ll be fun!”
Husband didn’t tell the aunt & uncle. Not my problem.
I got passive-aggressive lip about it from Husband’s aunt a week after Christmas. She made a snarky comment about how “It sure would have been nice to know that you guys were there. Why didn’t you come to visit us?” So I told her, “Well, you should talk to your nephew about that because it was HIS job to tell you where we’d be. And none of you guys could make a decision so we made other plans. Besides, would you really have driven 1.5 hr to our friends’ house?”
Aunt said, “Of course not. That’s too far for us to drive.”
Keep in mind that the route the aunt & uncle take to get to their cabin in the San Bernardino mountains basically goes near our friends’ house and it’s a longer drive to get to the aunt & uncle’s cabin than it is for them to get to our friends’ house.
So that’s fine. We were not a priority.
We all only get so many trips around the sun. I’m spending MY remaining trips around the sun in ways that reflect my own personal values. And I don’t bother chasing after people anymore who have shown time & time again that I & my immediate family are not important to them.
That being said, I totally understand why hoggirl probably wants to maintain marital harmony by coordinating a b-day celebration for her MIL. But I would not be inclined to go out of my way to make a big deal about it. Take MIL’s lead on this one. And it sounds like these days, MIL defers to Bob. So that’s fine. If Bob is the chief decision maker of their household, then ask Bob what the plans are.
And whatever you DO end up doing, EXPECT it to not be enough in your MIL’s eyes. And you know what else? You’ve been adulting for plenty of years to know that your MIL’s opinion of you does not really matter. You are a good & decent person. It is not your job or your problem to solve all of MIL’s issues for her.
You do not have to put up with disrespect just because she’s your MIL.