I can understand the desire to cohabit; it's something that I desire with my other partners very much, and always want to push towards. However, after a situation that went sideways because of living together and discovering huge lifestyle differences, I am WAY more cautious about it now (although I still desire it very much for down the road!)
I think the most important thing to consider is whether or not you have a true lifestyle match. Seemingly insignificant things can create a lot of conflict when you don't have your own space to retreat to. I've seen epic fights between partners over the craziest things - how to cut an onion, for example. Living together means that you're in each other's space all the time, and while it can seem like it's going to be a giant and amazing slumber party, it also opens up the capacity for a lot of problems that the relationship might not be stable enough to handle.
Questions: Is there a reason why you are all moving in together now? Have you lived with anyone before? What concerns do you all/you have about living together? Are there areas that you think that you'll do really well with? Areas that you think that you'll experience challenges with? What problems have you/they had with room mates in the past, and how did you deal with them?
For myself, I want be sure that living together will bring us closer to a partner, not separate us by accident. Sometimes you can think that someone is going to be GREAT to live with, and then you find out that things aren't as they seem. For example: My partner and I are extremely neat and tidy people and keep a really clean house. Based on our girlfriend's place when we went to visit her, and when she was at our house, we assumed she was too. We talked extensively about what everyone wanted before we lived together, and she came over all the time and saw how we kept our home and ran our life & participated fully in it when she was there. In theory it was great, in actuality it was a bit of a disaster. Keep in mind that we knew each other for well over a year, and had dated for several months before living together.
Moving in together thrust us into the reality that she had only cleaned the house for us before we came over as guests, but that she lived like a transient on a daily basis; clothes all over the floor, fungus growing in the toilet in her bathroom, overflowing litterbox from her cat that stunk up the entire basement, almost never vacuuming or doing pre-agreed upon chores that we had all split up. We talked about it, had house meetings about it, and in the end, just had to live with it, as it was truly her lifestyle and not ours. It was not an easy experience, and it definitely had a negative effect on our overall relationship, and based on our pre-move-in talks we never expected it to be like that.
Living together is a big step. A HUGE step. Co-existing and sharing a home is a big deal, and it ups the ante in the relationship. This can be a good thing, and communication definitely is at the heart of living together, but my concern is always whether or not your lifestyles ACTUALLY fit together.
For me right now? We have decided that extending individual living situations can keep things exciting and fun for longer, and that if/when we move in with another partner in the future we will definitely do a trial run before taking any big steps. We have talked about "half-renting" a place together so that we can share a space while still having our own home to go to with our present partner. I also think it's important to be well out of NRE and have at least one really solid fight/misunderstanding that gets worked out, so that you know you can sort out uncomfortable stuff BEFORE living together.
This might not be the case for you three at all! I thought I'd get my two cents in though, as my mindset has definitely changed around this over the past few years.