At first we thought it was the battery, replaced it after we checked (it was no good even after sitting on a charger), then thinking it could be the alt, so I wanna take the belt off to check. One issue, the tension is insain. I’m not sure what I can do besides either try loosening the alt first then tension or just cut the belt, which doesn’t need to be changed.
Ion know man.
Why do you think the engine is seizing? Because the starter doesn’t work? If so, I would focus on the starter.
If the alternator is bad but the battery is good, the car should start, or at least try.
It sounds like you should do some more diagnosis and thinking about the problem before you start cutting belts and taking the alternator off.