When SIL invites herself over

Husband and I are simply cordial to my S-I-L and her husband. However, there have been occasions where my M-I-L has her kids and they come over to play with my kids. My SIL takes it upon herself just to come over my house. She communicates only through a third party with me/us-using my MIL as the mediator. Not only is this rude for me but also annoying and childish.

I always ask my SIL personally if her kids can do something with mine or do invites.

I have a parent-teacher appointment tonight and asked my MIL if she could come over watch the kids the most for 45min. I said I know it’s the day you have my niece and nephew bring them with you so they all can play together. She cleared it up with SIL and she calls me back saying my SIL is coming too!!!

Mind you I have never been to my SIL’s house, when my LO wants to go over play with her cousins, my SIL pretty much says my LO can by alone or with Grandma.

This double standard is pissing me off and I’m not sure how to set boundaries that my SIL can’t just invite herself to my house!!!