Account Merging / Character xfer ?

So my brother wants to sell his account to my boyfriend who has an existing account. My brother and i have accounts with the same last name, boyfriends account has his last name. We were wondering if there was anyway to transfer the characters from my brothers account, to my boyfriends without having to pay for two accounts. Would it be possible for me to transfer my brothers characters to my account, and then merge my account with my boyfriends so we are only paying for our two accounts yet can both still access the characters from all three? Pretty much what would be the easiest way for my boyfriend to gain access to receive my brothers characters without having to pay for multiple accounts. Any help is appreciated, thank you.