When we arrange to see PIL who live a bit of a distance from us, it's a day trip, so I try and make it an outing. They actually really like this. I also do it because I have 3 DC from teens down and they can't sit around.
So, for example, if there is a castle we want to go to, a historic town we want to visit or a fete (all pre-Covid of course) I will arrange to meet them there. We will do the activity, have a picnic or lunch or get a nice coffee and cake.
Here is the issue. Whenever I do this, the first thing my MIL says is "are you going to invite SIL and her husband?" If I am not straight on it, she gets upset or a bit angry. SIL and her DH are 50+ and have no DC and live a couple of hours away from PIL.
I have invited them in the past but it basically spoils the day. SIL openly doesn't like me and I don't know why she comes. DH and I are not keen on her DH as he is really pretentious. They turn up late, end up influencing what we do and what we eat (it's got to be somewhere posh) and my DC get no time with PIL as they just fuss over SIL and her DH. We are basically taggers on during our own day out. I'm also sure that if I was allowed to sit and talk to MIL on my own and have a nice time, we would have a better relationship. When SIL is there MIL is mindful not to say anything nice to me or pay me any attention. I am having a pop at my SIL but she is really childish.
In the past, I have invited PIL on days out, meals out, weekends away, special occasions at our house, holidays, and every time she insists that SIL and her DH are invited. Of course, I am happy to do it sometimes but I'm sick of doing it all the time. SIL and her DH do loads of activities and days out and weekends away but don't invite PIL to any of them. They have never invited us to anything they do either.
Covid allowing, I'd like to plan some things for the summer holiday and a lot of these take us near to PIL's house. They will get upset if we don't include them and it enables me to kill 2 birds with 1 stone.
How can I say to MIL that I don't want to always invite SIL and her DH to everything we do and if they want to do things then they can invite them themselves. MIL will kick-off but it is either this or I stop including PIL. My DH won't say anything as he is too laid back. I know I have a DH problem here too.