My personal advice, is that if they pre-drink, you stick around and pre-drink with them. You don't have to consume alcohol with them, but just enjoy the banter and get to know them.
If you are that adamant about refusing to go to a party, there's not much more you can do. Just try to be around as much as possible in the settling in period.
I'd personally recommend pushing the metaphorical boat out and trying it out. I don't know your reasoning behind it, but there are multiple kinds of parties. Not every party is like the last days OF Rome, some are just chill and you could just ditch before they go out clubbing and at least our yourself out there abit.
I understand drinking isn't everyones cup of tea. Whether it be due to religion or personal taste, but try your best to mingle as best as you can while your flat mates are around, if you still refuse to even try going to a party.