What to do if freshman daughter comes home for holidays and basically lives with older boyfriend?

Not unless your goal is to completely ruin your relationship with your daughter over a romance that may or may not even survive. And if it does survive, content yourself with being the grandparents the kids barely even know.

I’m not saying you have to like the situation, but taking an adversarial position is not going to work in your favor.

If I were in this situation, I’d do what many are suggesting-let your D know that you expect her to be present a certain amount of time because she is a member of your family; but also because you love her and enjoy her company. If you have to invite the BF along for some of that time in order to get her cooperation, so be it.