Game of Thrones: Declaring a March to various adjacent territories at the same time
Answer 1 "Before resolving combat, all other non-combat movement from
the area assigned the March Order must be completed." GoT second edition rule book, page 15, 7th bullet point.

Answer 2 It is not the case.   "If a playerleaves an area vacant before initiating combat , he must decide whether or not to establish control of the area before combat begins" GoT second edition rule book, page 24, 4th paragrqph of "establishing control of an area"