I was going to just put the one way flights on my credit card and let them pay me back.
I think booking all together is better as the computer algorithms may bump rates up after 1st couple books. Also some advantages with "groups" in regards to connections and cancellations.
I would have immediate payment required from all parties (Venmo, etc) once you book. Likely include travel insurance in this amount as well. A group text can confirm all are in agreement to pricing after on airline website even before buying. Don't get caught being their banker!