Do you think they are true potbellies/mini pigs or just young commercial or heritage pork type pigs? Post some pictures if you have them!
I wouldn’t consider keeping them as pets if they are going to mature into 400-600 (or larger!) hogs. All pigs are destructive, even the small potbelly/mini pig types, but size does matter, unless you have enough land and literally don’t care what it looks like. In that case, you could give them several acres to trash inside a strong physical and/or electric fence. They will root the ground of any small-ish enclosure until is literally bare dirt/mud. Grass/foilage will disappear and and they will take out the root structure, too, until nothing holds that dirt together, if that makes sense. They will do the same to small trees and kill large mature ones by taking out their roots. If male, commercial type pigs might already be castrated since producers often do it themselves when the pigs are very young. It will be expensive to have a vet castrate an older, larger male pig even if you can find one to do it in the field. Mini pig types might be able to done on the farm by a field vet, depending on your local talent.
Female pigs can be fearsomely moody when in heat, which is often, and will (not if) go on to develop uterine tumors if not spayed. Field vets will not spay pigs, large or small, so plan on having to source (potentially far and wide) and then transport to a vet that is experienced and able to do this in a hospital setting. Plan on spending at least $500-700 for a routine mini pig spay and 1-1.5K for a large farm type pig spay without complication. Seems ridiculous, but it is definitely not at all. It is nothing like a dog spay. Pigs are very difficult anatomically (it is extremely difficult to gain venus access, for example) and also bleed like the proverbial stuck pig.
Some people do love their mini/potbelly type pigs as pets. Big personalities. I do not happen to love them, haha, but I respect that a lot of people do. Pigs can be aggressive with strangers or even not-strangers that they happen to decide they do not like and will bark, lunge, and attack. Basically like an unpredictable aggressive dog. My friend’s pig cornered the FEDEX guy on her porch one day, just for fun. The dude was literally almost hysterical and in near tears. The pig also legit bit is foot/leg and left bruises…that could have been a bad situation, honestly. Pig-o happened to love the UPS man. Go figure.
If you keep them as pets, feed them a pet pig specific diet (Mazuri is one brand, but there are quite a few out there now) vs whatever is labeled pig/hog/swine at the co-oop or feed store. Those are for commercial hogs and designed for growth/gain. Absolutely not what you want for your pet pig. They gain weight very, very easily. It is what they are designed to do and without longevity in mind. Keep them as lean as possible. Commercial pigs often aren’t really able to live out their natural lifespans before becoming crippled with arthritis and suffering from extreme mobility issues. Mini pigs, too, if let to get fat.
Large or small, pigs will need routine hoof and possibly tusk trims. Field vets can often do this for small pigs on the farm for you without sedation by simply flipping the pig over and doing it real fast while they scream their bloody heads off. If you cannot find anyone local to do this for you on the farm, plan on dragging them to a specialty hospital to have it done either same way or under general anesthesia at least once a year at minimum. If they will only do it under GA, plan on spending $400-500 for this service.
Good luck with the piggies. Like I said, some people love them. Not trying to discourage you from keeping them as pets! I do, however, feel like a lot of people have no idea how challenging they can be to keep…
The biggest issue with pigs is water. They are short, sloppy, pushy and like to create their own mud hole in the heat so a horse trough is too tall but they might dump something shorter. Food is easy because they will eat anything. Just feed a decent grain and give them whatever leftovers you have. If they are black, I doubt they’re a production breed so you’re probably right they are pot bellies but they could also be American Guinea Hogs, which will be larger but not several hundred pounds at maturity.