Girls on our lads holiday - am I being sexist?

Not sure about if we were excluding T - I don't think I have an opinion.

It sounds more like you have an objection to going on holiday with randoms you don't know, who may (and are likely to) have extremely different interests.

The sister thing is a bit odd (the age of the sister does make a difference - is it similar)?

Bringing your mum on a lads holiday is ******* weird. Does bullying not exist anymore?

So my friends (all 20) and I have planned a lads’ holiday to Italy in September and there was going to be our group of 5 boys but one of our female friends (T) wanted to go which we thought was fine but then she decided to invite her sister (who we know but not that well) because her sister always wanted to go to Italy! This secretly annoyed me because she didn’t ask. Then one of the guys doesn’t have much confidence so T suggested he bring his mum and she didn’t let it go so now his mum might be going. Then to top it off T is changing all the holiday plans to suit her interests.
I thought it was going to be our first lads holiday and now we’ve got 2 girls and maybe someone’s mum coming and I’m just really annoyed by it. One of my friends agrees with me that her domination over the trip is annoying but thinks not wanting the girls there is sexist. Am I really being that unreasonable for wanting a lads holiday to be a lads holiday??