Please explain in very simple terms

If you get the 12v cord for your C-PAP, you can run it off a good 12v jump starter. The jump starters usually have a 12v outlet. You may need 2 jump starters for two C-PAP machines. I believe some C-PAPs have accessory batteries you can buy.

CPAP on direct 12v uses less power than on inverter. If off-grid, why convert 12v to 110, then back to 12v??

Also 20+ years. Have used CPAP all night on two 12v coach batteries with no problem. I do not use humidifier when in RV. Knowing you brand and model of CPAP, plus your pressure number will help with a full answer.

I have been using a CPAP for close to 20-years.

Do either or both of you use a humifier ?

How old are the CPAP's

Your answers will help with suggestions, I could offer.

Couple options. Need to run CPAP can be done with 12v power direct in many cases. You need to check with your CPAP manufacturer if the proper adapter is available. Then you just need to get 12v power to where it is needed.

Or you can install a small sine wave inverter and plug into the closest 120v outlet.

Either way I recommend 2 to 4 batteries to keep the power on without worry.

Your RV dealer should be able to help you get this done if you are not mechanically inclined. Please post what the estimate says they are going to do so you know you are getting what you need. Not more, not less.

I am not fond of generators but another option is to run a Honda 2000 all night.

Here is some reading for being off-grid:
The 12 Volt Side of Life

Unless you have a generator, you will need an inverter to run off the house batteries. They are not expensive, a modified sine model will do just fine, but you will need to find a convenient 12VDC source to plug into. Both machines will run off one unit, they don't draw much power. I wired one in when I had the nose in our fiver apart to fix some rot, we are no longer dependent on shore power for my wife's CPAP. Talk to your dealer about the best way to do this.

My brother-in-law camps with us from time to time. We just fire up the Honda 3000 generator, put it on eco-mode and let it run all night. No problems.

We use a couple CPAPs and the batteries will last all night in the Foretravel but in the born free they will not so I just turn on the generator when we go to bed and not worry about it any longer.

Probably not. Depending on the CPAP you have and whether you use the heater or not it could drain a single battery in a few hours of use. With two machines you would need multiple batteries, and a good inverter. There are battery powered machines that could work for you.