Since you have two they are going to fight. Anostomus tend to be aggressive unless in a school of 5 or more. I am sure tank size could have some effect, but like I said just having 2, they're most likely going to fight.
Yes in fact they do eat algae as well as veggies, fruit, worms, fish food, etc. I have a pleco that loves romaine lettuce, snow peas, and zuccini stuffed with freeze-dried blood worms. Who knew haha.