OK, now we’re talking NCAA. There is a terminology difference, for certain, and there may be an actual rule difference, but I don’t know (I only know NCAA).
By rule, a B player does not commit a foul simply by entering the NZ before the snap begins. However, if his entry into the NZ causes a reaction by an A lineman in the immediate area, then he commits a (dead-ball) foul. If any other A player reacts, then Team A commits a (dead-ball) foul. So, there really can’t be simultaneous fouls. As officials, we simply have to decide what happened. Did B enter the NZ and cause A to react? Did A false start, causing B to react?
If we rule B fouls, that’s Offside. If we rule A fouls, that’s a False Start.
Unrelated to either of those is when a Team A player simply takes a position in or beyond the NZ before the snap. We always give them some time to adjust themselves back behind the NZ, but, if not, and the snap is clearly imminent, that player commits a (dead-ball) foul for Encroachment.
No simultaneous opposing fouls.