I think I know how we'll handle this but I wanted some input from others first.
BG: For the last 15 years, DH and I normally host TDay, Xmas, and Easter for members of both my family and his. DH has his mom widowed mom Sue, unmarried sister Marge and brother, Ron, who has been married for 7 years. Ron's wife, Doris, has a Mom and Sister who live in our city and have been invited to attend TDay, Xmas, and Easter on numerous occasions. The two times DH & I didn't host a holiday because we are out of town, Sue & Marge went to Doris's mom's home for the holiday. Also, Sue and Marge are closer to Doris' mom and sister attending bday celebrations and other events at their home.
Doris also has an uncle and his wife who've moved to our city in the last year.
Ron & Doris and their two little boys bought a new home this summer which means they now have enough space to host family holidays. I expected that they'd want to start doing some of the hosting, which we are perfectly fine with. end B/G.
All of my family members who normally attend TDay at our home have other plans. No biggie this just means that we are actually free to plan something different for TDay.
Yesterday, DH texted Ron asking if they had made TDay plans, as we sort of expected they'd want to host in their new home. Ron texted back "Doris wants to have TDay with her family at our new house".
Today I received an email from Doris, sent to her family and Ron's, with an invitation to their child's bday celebration for the weekend before TDay. In additon to the Bday for our nephew party invite her note said that her older brother would be in town for Thanksgiving and the party would also be celebrating his bday. So I know that she'll have the following in town for TDay, her mom, her sister and sister's DD, her brother, her uncle, his wife, and his DD. With their family of 4, that makes a nice size group of 11. If they include Marge and Sue into their group, it makes 13.
Based on the texts and emails we've receive to date, I am pretty sure DH & I and our 2 kids are not invited to their TDay. If they had invited us, we would attend because it would be appropriate. They have no way of knowing that no one from my side of the family will be with us for TDay so there is absolutely no hard feelings about not being invited.
So we are operating under the assumption we aren't expected/invited to their TDay celebration. DH will be contacting his mom and sister to confirm their plans. If they say they plan to go to Ron and Doris', he'll say "Sounds good, we just wanted to confirm". If they say they don't have plans, ie, haven't been invited to Ron & Doris's either, we'll invite them here. We can't mention to MIL that we don't believe we are invited if she and SIL are because she will have an absolute fit.
The reason I'm pushing on this is I want to invite a family that we are good friends with over for TDay. They don't have much family in town and they have a son who doesn't do well with big crowds but would be fine with just us and MIL and SIL. But I don't want to wait until the last week to invite them.
My only pause about running with this plan is that Ron and Doris do not always communicate clearly. (It's a trait of DH's entire family) Last year I sent a note out 2 weeks before TDay asking everyone to confirm if they planned to join us. I heard nothing from Ron and Doris so assumed they weren't. We get a text 10 minutes before everyone is set to arrive saying they are running late but would be there in time for dinner. Doris and I try to make our DH's stay enaged in the family planning and I'm sure she would have been appalled to realize Ron had not RSVPd. He believes if he mentions to his mom his plans, that it is then her responsibility to communicate it to us. While I've had 20 plus years to learn to do things like sending a note such as "Doris, I'm sure DH has let you know we'll be there on Saturday, I wanted to see if I could bring anything. Also, did he mention our DS has an activity and won't be with us?"
So if you've gotten this far, which I'll admit I've typed while having an early afternoon cocktail, is there another way to handle this?