Two accounts

Merging accounts to a battle.net account doesn't work like that. A battle.net account merely acts like a keychain for wow accounts and other blizzard games.

Each wow account within the battle.net is still separate and requires its own upgrades and subscriptions.

***Quoted for Turtle***

When merging two World of Warcraft accounts into a single Battle.net account you retain both of the original accounts, Doitforjohny. You are simply able to access them both under one Battle.net account. You wouldn’t lose any characters, or items. You would, however, still be required to keep an active subscription on both accounts, if you would like to play them both.

If you want to condense your playing experience to one account it would require you to transfer characters over to one single World of Warcraft account. The ten character limit-per realm-would still apply if this was the approach you decided to take.