Yesterday I finally finished my OpenSim environment again. There's two installs now on my server: a plain OpenSim install for the kids, and a Open Grid enabled one for myself. I didn't know for sure if two installs would work, but it seems to be fine so far.
It even seems you can run two installs on one database. I accidentally forgot to change one database value in the OpenSim install for my kids, which caused their content to end up in the same database as my OpenGrid install. Result: I suddenly saw my sons' newly built house pop up on my Open Grid island!
I'm planning on leaving the kids' standalone OpenSim alone for a bit. It's good enough the way it is; no need to upgrade every couple of days. That's what I can use my OpenGrid install for!
My son at his new underwater villa: