GTA V story mode question

How do you make money on gta V besides assassination missions and stock market?

Michael has 28k and franklin only has 5k because I bought properties And Trevor only has 140k. so how do I increase their money?

Yeah it took forever to start making real money. I made most my money off the stock market. Where I see stuff that is usually high, and when it is super low buy a ton.

There was some mission about this, and I don't remember if I was suppose to invest or not, but yeah I didn't get super far, I loved the robbery stuff and making teams, but basically everything else was just kind of not as fun as I'd like. Mainly cause I had to split everything I do into 3 characters, all my money, missions and stuff, with the few occurrences where I use all 3.

There's really no other way to make huge figures aside from making the right investments as influenced by those side missions. The stock market is otherwise useless and I don't think there are any other repeatable activities in the game that can make you big money unless you spent countless hours doing it.