Purse
Legend
I'm fairly sure you can link a p2p and f2p together so they become under the main Battle.net account. Contact Blizzard through support (open a ticket through the battle.net website is best way) and they will walk you through it if you tell them what accounts you want linked 
As for merging f2p + f2p accounts, I don't think anyone has tried that
As for merging f2p + f2p accounts, I don't think anyone has tried that