Is it weird? Read description please.

My sister invited my in-laws to her kids birthday party (which is being thrown at my place) without me knowing and has all the sudden started talking to them and adding them on FB after five years of not even saying as much as a hello to them. They probably won't even come but she's asking me to ask them for confirmation. Which I'm not comfortable with.

Her inviting them like that when she barely knows them and they're my in-laws not hers...Is it weird?

-On a side note she knows I have a touchy relationship with them as it is and them coming to my place gives me anxiety. But I know she wouldn't do it to make me uncomfortable. She just always seems to cling to my friends or the people in my life. Always has since I was a kid. She's 4 years older than me so I always thought it odd that she did that especially knowing she has her own friends her own age. Even my friends have said something to me about it being weird. But now this in-laws thing makes it even weirder for me.