I am not aware of a way to get more than 2 scripting clients to run at the same time for the same character. Multi-threaded scripts, sure. Orion and EasyUO both have multi-threading. Just 2 clients running at the same time, though? I am not sure of any setup besides UOSteam and EasyUO.
Most shards allow 3 accounts per player or household. Sometimes called "multiboxing," the "box" in tripleboxing is slang for a computer. Originally three computers, three keyboards, three monitors, 3 accounts logged in simultaneously on 3 clients with 3 scripting engines managed by a single player. Can be done with virtual machines these days or special tools.
Typically the player keeps most action on a primary character with hints whispered to the scripts running on the other two. When he needs the other accounts to take an action beyond the scripts' ability, he multitasks between them.