A single floor of a typical house or bunker can be considered to hold the same number of individual figures as a truck – 12. Assaults against multiple units on the same floor are resolved simultaneously against all units on that floor of the building. For example if there is a squad of 9 and a weapons team of 3 on the same floor of a building and they are assaulted by a squad of 10, the combat is resolved as if the assault was 10 vs 12.
Unit casualties are determined by the defender after all combat is resolved. Effectively this means that if the defender is victorious in the assault they can determine who survived.
Flamethrowers are considered to attack all units on the same floor of a building. For example if there are 3 units on a floor of a building, the flamethrower selects one target but resolves combat against all 3 units sequentially. Only a single die roll to determine if the building catches fire is made for each “firing” of the flamethrower.