Questions from a noob

So you have two things here.

One you can set up the parents to do whatever they want while you play the teen... but you need to set them up with autonomous jobs. Like business, cook, music etc. You'll still have to a bit of management from them because they will potentially get fired, promoted, be prompted for answers on the burning questions of life, and also bills need paid etc... There's even a toddler challenge where you start the game as a toddler and you do not switch from the toddler until they're Adults/Elders (can't remember how long people run the challenge) so you can play without having to guide them much if at all.

The second... you can't separate their money from your teen without the teen living in his own household. There is one possible solution that I haven't tested that could work is making them roommates if you have Discover University. Your parent set up a thing for a "roommate" and the teen accepts. Or the teen could and make the parents pay them... Alternatively, you could just buy some really expensive build items and put them in your build inventory and not touch them so that there is little money for him to mess around with.