rookie questions

[clarkmj111]

I am probably going to be a pest for a while - i have had a huge collection of PG (acquired second hand in 2017!) but only just started playing
also only just started playing Inf Attacks too
my first question relates to move to assault.
the rules kinda say move one unit at a time (not a stack) EXC =- attached leader.
is this also true for an assault move?
a stack of 2 units has to assault one at a time separately? or can a leader take both in?

this specifically came up with a cavalry charge - but i guess it applies equally to a 1 hex move

help? thoughts?