MIL cannot accept it...

My MIL mentioned a few days ago how my SIL with family are coming for a short visit on Sunday because it's our nephew first birthday. And if we want to come by as well she's baked a cake and having snacks. My husband said no but she's insisting, mainly because she's desperate for the siblings to get along after a fallout last year. SIL wanted that my husband be involved in her house renovation and he nicely declined, refered someone else. Ever since she's been a miserable bitch and stopped talking.

First off, my SIL is visiting her parents and it's a bit strange to waltz in. Second, she has no interest to have a relationship with us whatsoever. And third we found out our niece isn't allowed to come over our house (just because she's an ignorant twat) she's involving kids not to have a relationship. She takes no interest in our toddler, doesn't talk to her at all and clearly doesn't want her over to play with her cousin. And here is my MIL trying to butt in and fix things. However, my husband said he's totally forgotten about the birthday and that we have no present, I think since they don't want their children anything to do with us, there is no point in forcing a relationship just because you're an uncle or aunt. We only get to see them at my in-laws by chance, if it wasn't for them we'll never be able to see them. I find that we're just stooping below their level by trying hard if we show up and give presents without any invitation! Am I wrong?