WIBTA if i get strict about my friends not paying be back?

Ok so earlier this year in June i bought tickets for myself and 3 friends to go to a muscial festival in November this year. I also paid for accommodation for all of us +1 other friend who paid for their own ticket. All up this cost me about $1000. As soon as i had bought everything i let everyone know how much they each owed me as well as all my bank account details etc etc. That was in June. Since then i have asked them a further two times to pay me in a group chat we have. Only 1 of them has paid me what they owe and another has said they will pay me incrementally but they didn't say over how long or why just that "they couldn't pay it all right now". That was at the start of July and they haven't paid me anything yet or given me any further info on their increments plan.

I am also kind of pissed off at one friend in particular who, since June when i bought everything and asked to be paid back, has told me she is going to go to Europe for 3 months and has recently booked flights, all before paying me back. This is all on a whim she has told me, just flr fun, as she doesn't go to University at the moment and only works part time.

Some further info on the friends who still owe me, yes they all work and 2/3 of them attend uni and im pretty sure they all deferred their fees (meaning they don't have to pay for each subject/semester up front).
Some further, further info that may help- my older brother did the same thing with his friends for this music festival; bought the tickets and accomodation and all his friends had paid him back in full by July.

Some of my other friends have told me i need to be stricter with how i ask them to pay me back but i don't know how i can really force them too. Other people have said to threaten to re-sell the tickets or make them pay me more for the ticket before i give to them but that sounds like extortion to me so i don't know.

WIBTA if i try and be stricter somehow? Or should i just wait and trust they'll pay me back soon.

(Pre-emptive sorry for formattimg, am on phone)