There’s nothing stopping you having two separate BT accounts, billed independently of each other , both in your name , and paid from the same bank account, but I doubt in a residential setting you can have both services combined into one BT account, where the costs for each individual service are combined together, and then paid for in a a single transaction, that’s more of a business type situation.
Apart from having two payments made to BT instead of one , there doesn’t seem to be any other advantage in trying to combine two accounts into one , simply take BT service at your new address and pay for that separately while continuing to settle the bill ( presumably in your name ) at your relatives address .
