Having problems with our pool. I'm confused and need help

[Rhavoreth]

Hey all,

My wife and I just moved into a new house with a pool and we are having trouble figuring out how the pump system all works. We have a maze of pipes running into 2 pumps (one of which is broken and needs to be replaced). I am pretty handy but for the life of us we can't figure out how this system works:
Pictures: https://imgur.com/a/TCyBLLI

- What position do the handles need to be in for normal operation
- How can I isolate the water from the broken pump (one on the left) so I can replace it
- If the pool gets too full (rain in FL can get intense) how can I drain it.

I've marked on the overview images some of the worn labels that were on the pipes, and if its useful, the pool has 2 drain covers next to each other at the deepest point, a single skimmer, and 2 filling points from a water feature and a hot tub thing (heater is broken for it though so its just a tub)
Thanks a lot for all your advice!

[Teapot]

Wow! This sort of work is what I get paid for.
You don't at the moment have the option of a normal operation, you only have run sufficiently to get someone to buy the home!
From the look of the valve positions on the broken pump (shall we call it Pump1? ) it is isolated, the 3 way valve to the right of the one marked skimmer is in the closed position. Also It looks like the pump is above the pool water line. At the moment broken pump 1 is the only way you can filter and chlorinate the water so you MUST add chlorine manually. The filter is a small cartridge filter and not a sand filter. It is common in the USA to have to larger unnecessarily powerful pumps and far to small a filter, just the way you guys seem to do it and then moan about the size of your electricity bills! Maybe you would consider some alterations?
On some skimmers, there is a port at the top near the lid (hardly ever used by dumb pool builders). If that is utilised, it will allow water to drain out if the pool gets to full.

Pump 2, the one that is working, as far as I can make out from the photos, just circulates the tub/spa and spills over into the main pool which at the moment is not filtering so nasty dirty and unchlorinated.

I hate installs like that, the reason you need big pumps is due to bad plumbing, to many knuckle elbows, to smaller dia pipe work.