Only tweeters work

I know this is a very common issue.
I plan to replace my radio (mine is the most basic) and upgrade to one that I can play music from my iPhone. My vehicle originally came with a backup camera, the bar above the license plate was replaced and doesn’t have it, along with the rear view mirror being replaced. On two occasions, my drivers door speaker worked. I’ve seen videos of how much water comes out when you unplug the connection to the door and mine did have a lot of water. Should I assume that because the door speaker worked (only lasted a day each time) that it’s not my amp? I do hear when my blinkers are on. I need to add the backup camera, but seen that many new stereos include it. My tint is so dark, I have to roll all windows down to reverse at night. It was purchased used, didn’t notice the issue until driving off the lot, but they never worked. I’ve read many posts and most replaced the amp. I’ve already checked fuse. Radio does work, just no sound other than tweeters. Before going to a place that will charge me hundreds, where should I start? With so many issues I need to address, I need to be a bit frugal with spending money. Toting 4 children and no sound? I’m sure any parent can understand. My brother in law can easily do all the work. I’m just returning to work after taking a year sabbatical. We decided that filing a lawsuit would just add stress, so I accept the fact I was scammed, could have been avoided had I done research before purchasing used from an independent LLC dealership. But, should I start with like wires? I’ve never needed more than what came factory, so not needing fancy stuff, other than the stereo itself being upgraded to a touchscreen. The vehicle had to have been in an accident, despite not finding any records of one. Seen videos on sliding your hand/fingers along seams/trim to ensure they match, I realized it didn’t now that I know how to feel for things like that, I’m stunned when I look at the back, how did I miss something so obvious? (Face palm)