Fake Brother In law and his wife!!!!

So hopefully I don't make this too long....but here's a bit of background. My husband is the oldest of 3 brothers his middle brother got a girl pregnant at the age of 14 or 15 and they got married. So by the time I became a part of the family this girl had already been part of the family for about 4 years. Well we got married and sadly my mil fell ill and passed away During those last few months we became close and she relied on me to help her because in her eyes I was experienced ( I had taken care of my mother until her passing away) I helped my mil as much as I could. Well after her death I took charge of the house hold (I'm 26 and the other girl was 19 at the time...) so right before my mil passed the other girl got mad at her and asked why I was the one helping if I was so new and d idnt really know them.....to which my mil responded that she loved us all the same. after all we were her daughter in laws. Eventually I started cleaning out the kitchen and my fil remodeled it. I feel that my husbands sister in law doesn't like me at all I have been nice to her I tried being friends with her but nothing comes out of it!!!! she is expecting her second child and because I'm her sister in law I feel pressured to make her a baby shower....granted it's a collab with the other ladies from church and all I'm doing is the invites and buying the cake. my brother in law is the same . I have come to the conclusion that they are the way they are because they missed out on being regular teens with out responsibility. as for my husband and I we went through all the stages of going out and doing as we pleased and finally got married. they go as far as doing the same things we do or at least trying. for example if we go out to eat at say IHOP they will go ther ether necmxt day or if we go to dunkin donuts for early donuts and coffee on a Saturday they will go there later on in the day. we recently had a closet made and there they go remodeling the babies new room. I know that y'all will probably tell me to move out and we are ....hopefully by this summer. but my question is will they ever change? Or should we just stay away and have as little to do with them as possible in the future. sorry for it being so long but I just needed to rant.