How should a person deal with you if they don't recognize who is front?
Ask. Be sensitive to the situation however (cf. the comments about name usage in Naming Names) and of course any prior agreements you have with the collective about such things.
In the cases where the person has a collective name, use that. Assuming it's unique (ie. none of the members of the collective also share the collective name), it's a good indication that you don't know who is front without being demanding about it. Which gives the person concerned chance to introduce themselves if they wish. That doesn't work so well if the collective name is the body name.
Now, what if the person fronting also doesn't remember them?
Be reassuring. Just as the situation may be uncomfortable or disconcerting for you, the situation may well be the same for them. Introduce yourself, ask them if anyone on their end can give them more information on you, vouch for you, or at least verify your identity.
Despite all this, they may wish to part company, if they do, make sure they know where they are, and how to get to a familiar place, from which they will be able to get home if need be. A minor tip, refrain from giving them directions to their home unless asked; a stranger rattling off directions to one's house can be, to say the least, disconcerting.