So here's my plan based on y'all's comments:

1. I'll turn of water to the house (shut off is in the garage.

2. Fill the pool to the top and block off overflow drain.

3. Have son come by once a week to check pool. If it needs water to stay above the skimmers, he can turn the water to the house back on while he adds pool water. Then shut it off again.

4. Turn off off tankless water heater.

Am I missing anything?

Thanks for all your advice!

I turn ours off but not the tankless water heater. Been doing this for years. Is it actually doing something to the tankless heaters? Not sure how to turn those off.

Yes