Why do you want to sneak anywhere?
When it comes to movement speed, the controlled character determines movement speed - so if you have a scoundrel moving at 4.00, Madora's 0.9 speed is irrelevant and she will keep up.
Generally you don't want to sneak past monsters because you want to kill them for XP, the game isn't designed to reward you for avoiding combat - it rewards you for conning monsters not to fight you with rock/paper/scissors THEN turning round and killing them!
As for group sneaking, it's more your choice of formation that'll determine where the group members will be whilst sneaking - so ensure you use a group movement that best suits your current sneakuation.
