As long as the cells are the same basic chemistry it should actually work just fine. Just keep in mind that your maximum current will not totally add up. The two matching 100 amp batteries (1C rate 100 AH) will share pretty well, so you might be able to pull 180 amps from the pair without a problem. The 280 AH cell are probably good to 0.5C (maybe more) that is 140 amps. But if it does not share perfectly, you might only add another 100 amps. So that brings you up to 280 amps from your battery bank as a safe estimate. If you need more than 2,000 watts on a 12 volt system, then you will need to be very careful about balancing the loads across the different batteries. If you will be running under 100 amps (1,000 watts) then you don't have to worry about it. As flat as the discharge voltage curve is on LFP cells, there is still a constant curve slope. So let's assume you start with all of the cells near 50% as the sun comes up to charge your batteries. If you get 30 amps of charge current, it will start raising the voltage of all 3 4S battery strings. The cells that are at the lowest state of charge, will have the lowest internal cell voltage. That will cause that battery to pull more current. The battery that is at the highest state of charge will be at a slightly higher internal cell voltage. That will cause it to pull less current. The end result is that they will self balance as they charge up. As the first battery comes close to full charge, the internal voltage will start to spike up. But the terminal voltage can't rise, so what happens is that battery will basically stop getting charge current until the other cells catch up. They will all naturally top balance like that. When it comes time to pull current, the reverse will happen. If the cables don't match, and the cells have different internal resistance etc., it is very likely the 3 different batteries will have different amounts of current coming from them. But again, they will self balance, as long as the maximum current of any one battery is not exceeded. This is why you can't just add up the current capacities. As the current increases, the highest state of charge battery, with the lowest resistance cables will provide most of the current. But that will cause that battery to start discharging the fastest. It won't take long at all for it to come down to where another battery starts to pull more current. They should all find their sweet spot and share part of the current. The current might differ by 20%, and the state of charges could spread a little in the flat part of the curve, but once again, if you do run them to the lower knee, the lowest state cells will drop out and stop supplying current until the others catch up.
Fuse each battery at or below it's constant rating, and make sure you never pull more than about 75% of the total, and you should be fine. Adding different batteries is great for getting more time, but don't expect to get more peak power. I have 2 matching strings, and I still use this rule. I have each string fused at 125 amps, and the two together fused at 175 amps. And I would also recommend always staying well between the upper and lower knee voltages. Maybe charge to the top knee once in a while to help top balance the cells from time to time.