Social guidelines and Poly don't generally mix well.
What you need aren't social guidelines. You need personal guidelines.
If they are both aware of and comfortable with one another I think that one thing to consider is "time and place".
I think it's reasonable to be on a date with ONE and friendly with the other sometimes, and vice versa. I also think it's perfectly ok (IF all three of you are ok with it) to be on a date with both of them at one time.
I think it would be helpful for the latter if they were friends.
Are THEY interested in meeting one another?
I have a V-certainly NOT a triad as both men are straight. I dont go out on "dates" with both. When the three of us go out I'm with one in particular (and there is no vice versa). That is just how WE have chosen to do it. It does help A LOT that they are becoming friends though-so we can be sure to cover the details for everyone's needs AND both of them have said it's easier for them being in this situation as friends then it was when they weren't....
I think you need to ask if they want to meet. If so then sit down for dinner together and say "joe this is john and john this is joe" then eat and let the talk go as it will. Later you can get into deeper things-but first just hang out together. Let them talk about whatever things they might be interested in as people.
As for outside not so close friends-it's all about how comfortable you are. I don't give a rip who knows I have a boyfriend. Boyfriend doesn't either. But DH does care. He has people he feels it important not to have know. So we don't encounter them in any way that would suggest the situation.
IF none of you care what these "friends" think-do what feels right and screw 'em. If they care they need not socialize with you anymore. IF you do care what they think-don't set yourself up for problems with them.
TOTALLY up to the three of you.
"Love As Thou Wilt"