Threesome if not fully bi?

I’d love some advice on a current situation of mine. A good female friend I’ve known the last few years (and who lives only a few houses down) has hinted several times at wanting a threesome with us and her husband. I find the husband attractive and I’ve caught him looking at me frequently, and I assume they’ve discussed the prospect amongst themselves. Actually I know they have- she’s mentioned before he expressed interest as well.

Firstly, is this too close of a physical proximity, as in shitting where you eat kind of thing?

And, while I am attracted to women and my friend is gorgeous, I don’t necessarily want to go past kissing/upper body touching with another female. Does that preclude this situation from happening? And excuse my ignorance but does this make me bisexual at all? I was just curious if other women would expect a full bisexual experience from the other female.

This would be a first of its kind experience for me, just wanna get a sanity check lol. Go easy please!!