Same effects don't stack (Whitemage HoTs do stack...),so both AST having the HoT stance doesn't work. But the shield and the HoT do stack.
And with 2 AST in one group you have Essential Dignity twice as fast for single target burst damage and you have a greater chance to get raid-wide buffs. So it is not all bad with 2 AST in one group. I do wish that the HoTs would stack like the Whitemage HoTs do, but okay..
