Welcome to the RVForum. Stu gave you good info. All motorhomes that I'm familiar with have charging systems that enable the alternator to charge both the house and chassis batteries simultaneously, but different manufacturers often design their charging systems somewhat differently.
Our system, for example, is controlled by a Battery Isolation Manager (BIM) and it doesn't allow the alternator to charge the house batteries until they get down to 80% SOC, and only then if the chassis batteries are at, or near, full charge. There are other charging systems that have different charging parameters.
If your alternator isn't charging your house batteries at all, your battery isolation solenoid may not be functioning probabaly, there could be a wiring problem somewhere or...? It depends on how your system is designed.
Kev