Sorry to say, it's just going to get worse as they grow. They are extremely territorial with each other.
Can be kept with other plecs as long as the tank is large enough and the adonis is not the largest pleco, otherwise it will beat up on all the other plecos.
Not as big of a problem as juvies provided you provide enough DW to allow them to carve out territories. I've kept multiple juvies in a 60 gallon with no real issues. They are significantly more dominant than most other plecos, and because they're so spiny they can do some real damage. Unless you have a swimming pool, I wouldn't recommend keeping multiple larger adonis, though.
Very fun to have three. I'd split them up into separate tanks and grow them out until you can tell males from females. Maybe you can set up a 1000 gallons somewhere to spawn them. That would be awesome.
Well, they grow an inch per month until they hit about 10" so it shouldn't be long. Best of luck whatever you decide to do. Of course, the bigger they get the more $ they are worth. One of the few fish that holds true for.
a inch a month sounds good,i have been feeding them algae wafers and sturgeon pellets , i heard their growth rate is slow , i never seen any reports of it been breed in captivity , is it possible?