Well, to visiting the ILs to be specific.
I have been with DP for 5 years, have 2 DDs aged 3 and 8wks. I have never met his mother, despite her living just over the channel. I have met his stepfather a couple of times, as he has popped round whilst in the UK on business.
I do not understand why DP's mother has never visited, or why she has never sent a card or present for the girls. I don't understand why she does not call him on his Birthday or at Christmas. I don't understand why she did not call at all when DP decided to stop calling her to see if she would ever call him. They have not spoken for about two years until May when his stepfather had a stroke (now recovering). DP flew over and the relationship seems to have thawed a little, but he isn't really saying much. I know he enjoyed going to see his family though.
He has told me stories of his childhood which have made me a bit
about the way his mother treated him (cold showers as a punishment? WTF?).
Le point? Of course. DP's stepfather emailed a couple of days ago to invite us over for a family reunion. DP's mum is now reconciled with her elderly estranged parents and has decided that everyone should come to France for a get together. In two weeks' time 
-Baby DD does not have a passport
-I have my Uncle's funeral to go to the day before the 'party'
-We are skint
-I have never met her
I feel that she has shown zero interest in me or my children- or my DP for that matter- and I am simply not prepared to drop everything and fly over to France because she has snapped her fingers. I am not going. 8wk old DD is certainly not going. However, DP wants to go and take DD1 with him.
I feel uncomfortable with DD going to stay with people I have never met, and who are strangers to her. She doesn't speak French. However, her dad will be with her. He's so proud of her and wants to take her to show her off and I don't want to put my foot down and say she can't go- she's his DD too. But I'm not OK with her going either.
DP says he won't go on his own- partly because he doesn't want to leave me alone with the girls for a few days, partly because I think he'd be embarrassed to go alone.
So AIBU to insist that she doesn't go?