A couple things; if you have a 6 or12v system your batts should read about 12.7v per battery in total when fully charged. If your reading that low 6.7v, your math is fuzzy (two batts @ 6.7 + 6.7 = 13.4v) . To test them the cheapest way you need a Mighty Max Battery Hydrometer Tester Acid Electrolyte Lead Flooded | eBay
like this. That is the cheapest and most sure way to tell you what each cell charge is. Read this The 12volt Side of Life (Part 1)
that will help you get up to speed on the battery side of your RV.
Remember this general rule, in newer MHs they have a BCC (battery control center), that takes the 110v (shore power)or ALT 12v (in flight) current and manages the charging of both your coach and chassis batteries. If your not getting a charge to your house batteries, you need to check your fuses first. You should hear the iconverter fan kick on when it is in its charging mode of the battery system. Hope that gets you in the right direction.