I think bulldog plecos are typically supposed to be housed in groups, but I could be wrong.
You definitely have a 'common' pleco, which is the big kind. If at all possible, I'd look into rehoming the big fellow. Bristlenose plecos will get around 6" long, if that, or you could try a twig catfish. Twig catfish are about 7" long at full size, but they're very slender and mostly tail, so they don't take up much bio-load space. They'll eat algae and will happily devour veggies or nori when the algae runs out, plus they're awesome-looking and very gentle. I suggest you look them up.
I hate hearing people say "it's only a $3/$5/$1 fish/shrimp, so it's ok if it dies, I can just get another." It's still an animal! All animals should be treated like they're worth $10,000.
29 sw: Damsel, shrimpgoby, pistol shrimp, waspfish
65 fw: Rummies, glowlight tetras, pencilfish, darters, ottos, f betta, goby, dwarf gourami, ninjas
29 fw: Chili rasboras, pygmy cories, P. Gertrudae