This is one of those questions that is tough because of all the variable between different coaches. I personally haven't seen any class A MH with only two house batteries but I'm sure some of the cheaper ones may. Most have either 4 or 6.
I would assume for the pets you only need to have the inside temps around 65 or so which makes the heat demand fairly low. Heaters do take a fair amount of power to run so it's kind of a crapshoot.
If that is you lifestyle installing a genny auto start might be ideal so if the batteries do get low the genny starts and I believe they can be set to run for a predetermined period of time an that shuts off.
Dick
2002 43' DP Beaver Marquis Emerald Cat C-12 505 HP, 1600 Tq
2003 Jeep Grand Cherokee Overland ---toad