I think the easiest most effective method would be to tell SIL ahead of time on the phone. I think an invitation would be too subtle for SIL. Since saying something over the phone is scary to the OP, turning either of them away at the door isn't really likely to happen.
The part that would really annoy me would be SIL basically using me as a free restaurant to visit with her friend. It sounds like SIL is physically there, but really more interested in spending time with the friend.
I have a hard time being direct, and standing up for myself. As a kid I became fluent in passive aggressive so that I could vent frustration without being overt enough to get the stuffing beaten out of me.
I did end up calling SIL this morning. I started by saying that we're looking forward to their visit, and asked what her plans are during her visit (almost a week) and told her that I would love to get the kids together in addition to the Baby Blessing on Easter Sunday, but I know that she's always so busy. We chatted for a while, and I specifically asked her when is she going to get together with Good Friend and her kiddos. She didn't have plans yet, but was sure that she would find time. Then I took a deep breath and told SIL that I hope she gets a chance to visit with her friend, but that GF isn't invited to the house on Sunday. At first she was indignant and confused, like why was I even saying that, SIL would never
invite GF to a Blessing luncheon, that's for Baby. I brought up the graduation party and she pointed out "that was at a park." So apparently SIL would never invite someone to an event with a GOH, but anything that happens at a park is open to the public.
Shortly after that 'the dog was getting into the garbage can' so I had to go. I'm glad it's done, but now I'm stressing out worrying that either 1. MIL will call and tell me how sad SIL is; 2. MIL will call DH and tell him that I really upset SIL; or 3. SIL will call DH and ask why I hate her so much.