Welcome to the community. Looking forward to seeing and hearing about what you are getting up to.
Good for you taking in these fish.
As to feeding plecos, it really depends on how big they are. They will eat algae that grows in the tank, and on top of that feed them algae wafers. A full grown BN maybe 1 wafer per night, and supplement it with a slice of cucumber or zucchini 2 or 3 times a week.
A full grown common can get to 24 inches, and their diet changes as they get bigger. If its a similar size to the BN, then feed it similarly. As it gets bigger you will need eventually to switch to a more protein based diet.
You also need driftwood in the tank for them to munch on as it assists their digestion.
How big is your tank? Unless its in the 100 gallons plus category you would be better finding a new home for the common, or you can plan on an upgrade. Any other fish apart from the plecos?
While 100 gallons is minimum, to care properly for a common pleco for its full lifetime you really need 150 gallon tank, 200 gallon would be better. They grow into monsters and live 20 years +.
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