Your love for this couple is "new," you say. How new?
Are you all bisexual and sexually involved in every direction? Or is it hetero and you are with both men, the men each have 2 women, the other woman has 2 men?
What if you fall out of love with both members of the couple? (If you are bi.) Or the one member of the couple if that is the case? But your husband stays in love with his OSO(s)? Will you be able to continue being a part of this where he still has one or two OSOs and you only have him? Or will you want to run some sort of veto, that if you fall out of love with your OSO(s) and he doesn't, he has to break up anyway, make them move away, go no contact, or remain platonic friends even if you can't stand the sight of him/her/them?
Just saying " 'We' have fallen in love with another couple" isn't clear enough. You are all individuals, able to fall out of love with any one individual at any time, causing all kinds of ripples of anguish for everyone involved.
It is highly recommended no one (even mono couples) ever move in together until you've dated at least a year. Before that, your mind and body are awash in new relationship sex hormones, causing a bad case of rose colored glasses. We idealise our new partner(s). Also, every friendship is tried and tested by weathering a few crises together, such as: illness or injury, job problems, kid issues (if you have them), issues with older relatives' health, even things like a flooded basement. Will your sexy new partners be there for you in a clinch, and vice versa? It would be safer to find this out before you all start cohabitating. Nothing worse than a fair weather friend.
Definitely share the books Tinwen recommended between you and your husband at least, if not with your new partners. They will cover the issues I mentioned in great depth, as well as many other pitfalls you'd do best to educate yourself about before doing something as drastic as getting a place together with your new partners.