>>538302759
Normally she only stuns with her passive, this means her active attacks can also stun enemies for 1 turn, and if it's the first time you stunned that enemy in a battle the stun is increased to 2 turns.
>>538312061
For Andoris, it varies. Always put down turrets on turn 1 and if they're about to die (you heal them by replacing them), then prioritize throwing skill2 on enemies. Ult is only needed if PCharge is about to run out (it won't if you have Jiangyu) or to proc Allay Support when an enemy is gonna drop a strong AoE attack. Her damage output doesn't matter so don't worry too much about "not using CDs".
For Belka, use Ult whenever you can and go skill2->skill1 whenever you can't.