There's a big difference in scale between powering everything from an inverter and powering a TV (and video box) from an inverter, as you realize. For just the front and back TVs, the simplest and cheapest approach I think would be to have two little inverters that use a lighter plug to connect to the DC sockets that are there. It would not be a bad idea to replace the televisions with newer ones particularly if they're CRT televisions or if your friend would ever like to watch over-the-air television broadcasts.
Coffee makers, being heating appliances, tend to be fairly power hungry, though the exact requirements do vary considerably. Some small personal ones are around 300W, while some of the Keurig models use over 1500 watts.
While there is a transfer switch for the generator, you'd need an additional transfer switch for the inverter (or else set things up so that the shore power cord plugs into a socket powered by the inverter, which is more or less equivalent) in order to power the entire coach from it. You also need to remember to turn off various things, such as the converter and water heater (if electric) and air conditioner and usually the fridge. A more foolproof approach is to segregate the AC circuits in the motorhome and only switch some of them over to inverter power using some manner of transfer switch. Many larger inverters have a transfer switch relay built in. All in all, it is a significant project, doubly so if the battery bank must also be enlarged to reasonably power the inverter.
Using the generator for the coffee maker or using a non-electric stovetop coffee maker of some sort is in many ways easier. There are endless threads here on coffee making equipment. I find it hard to have too much of a preference myself since I personally find the taste of coffee rather revolting, though I do enjoy a good cup of tea.
