I strongly suggest finding a way to live in separate homes.
You were all scraping by before, and if this doesn't work out, you'll all have to figure out a way to scrape by afterwards.
The pressure of being "stuck" in that situation can put too much strain on the relationships and make it impossible to cope. No one will have anywhere to go if someone needs space.
No one can afford the rent all alone? Get roommates. Different roommates in different apartments.
It's hard enough learning to cohabit with someone when you've had a smooth relationship and everything is hunky-dory from the get-go. It's hard enough to learn to have a poly relationships when you have your own homes to get away. Throw those together and you're asking for trouble.
Gralson: my husband (works out of town).
Auto: my girlfriend (lives with her husband Zoffee).
The most dangerous phrase in the English language is "we've always done it this way."