K.B.
I usually set up the family togetherness on mother's day, for myself, my mother and my mother-in-law. We either do a lunch or a dinner all together, some years it is the men cooking out at so-and-so's house or we go out to eat.
If a group gift is gotten for my mom I organize all of us kids on price and what we will get, then I go get it... this year I told everyone they are on their own because I was super busy with work (but said flowers are a good idea). Thankfully my sister-in-law is super organized and always has something in mind so mother-in-law gift is usually taken care of by her.
I planned out my Mother's Day - went shopping bymyself (got a new outfit), had some togetherness, then dinner with the family (all the moms & their families), had some alone time to relax, read a book and take a bath and kissed everyone good night. It is what I wanted so I just told everyone and that is what we did :)
Oh and I would just tell the the kids that this is my day so we are hanging out together as a family, no hanging out with friends today. You could also say from such and such time to this time is JUST family time, you can hang out with friends before or after.