Main line passes through fuse box

I don’t want to sound to negative but in the USA this is absolutely against all electric codes.
In fact, if it were my house, I wouldn’t sleep well thinking about all the things that could go wrong.

As you pointed out with the arrows, the top of that photo goes to the 200 amp breaker.

According to this chart:

You would need a 3/0 wire size to carry 200 amps
As clearly can be be seen, your wire from the breaker is only 2/0 , according to the table rated for 175 amps at 75C (because of multiple wires together in same conduit).
But because that is a short run, i wouldn’t be too worried about that.
But the split after that is totally illegal/worrisome.
If all wires from there would be 2/0 i wouldn’t be so on the edge. But you can clearly see there are wires that are significantly less in diameter.
Breakers are there to protect the wires from catching fire.
The fact that you are now also feeding solar from behind this junction means that your 200 amps from the breaker plus whatever amount of amps from your solar could go through those smaller diameter wire.
Recipe for disaster. It will burn down your home and when the insurance sends an inspector, you won’t get paid a cent !

I know this is not what you want to hear, but this setup is really unsafe and should be corrected.
Instead of this box, install another load center with breakers and use appropriate size breakers for each ot the cables going to the sub panels.

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