Slitherine

From the Building FAQ

"If not moving along a road in column, a unit may only enter a building if they begin their move in at least in partial contact with it"

(a) SO units can only enter buildings (unless march column along a road) if they start there move already at ;leaf in partial contact with the building?
(b) Does this apply for assaults?
(c) How many units can assault a building? can as many as are in position regardless that only one can enter (if successful)

(a) SO units can only enter buildings (unless march column along a road) if they start their move already at least in partial contact with the building?

Yes

(b) Does this apply for assaults?

No - The assaulting unit cannot enter unless they force the defending unit out. Therefore they only have to move into contact with the building (and the enemy defending it)

(c) How many units can assault a building? can as many as are in position regardless that only one can enter (if successful)

As many as can physically fit. The defending unit will fight with 4 dice against each attacker though, so you could end up with a lot of disrupted units.
If the enemy are forced out, you choose one of your units to advance into the building.