It's best to start with your local authorities regarding the septic. Each region has very different standards. In some cases, old septics are grandfathered in and cannot be added to, or new ones installed.

Keep us informed - I'm curious as to what you find out. I like the idea a lot.

I'd def. ask there for some opinions.

and this looked helpful:
https://rvblogger.com/blog/rv-hookup-at-home/

You connect a hose from the house for water and set up a plug,preferably 30 amp for power, then need a connection for the sewer line, to existing septic system, you can leave the grey water(sinks and shower)connection open but leave the black water(toilet) connection closed and only drain as necessary...use additives to both tanks to keep odors down and help digest sludge.. that is basics. Also may want to add a skirting around trailer to keep winds and such out of underneath...especially if a fifth wheel as the bedroom will be in the upper area...local ordinances will come into play... ie permits and inspections

That is basically it ..

(on edit) also probably want to take tires off and store them so they won't rot ...

thank you. Yeah, I envisioned taking tires off, not so much for tires rotting (which I didn't know about), but to accommodate my mom's need to remove stairs as much as possible. Having grown up living in a mobile home, I definitely understand the value of adding skirting. And even though I don't have to do this in my house (I'm in NC and it can get very cold but not like northern states), I would imagine I would need to let a faucet drip in the RV to avoid lines freezing.

I located it next to the driveway so that I could reach it with the tank hoses. I have a hose bib and 20 amp receptical handy to it as well.

Your challenges will be more bureaucratic than technical. You can direct-bury underground-rated wire to a 30 amp x 120 volt outlet box on a post adjacent to the RV. PVC or PEX (very good for cold weather) can be run in the same trench for your water supply.

I had just started learning about the "clean out" thing before seeing your post.