This is often the case with preterm babies as they were born before they were developmentally ready to breastfeed efficiently. Preterm babies can and do learn to breastfeed, but it may take a little longer than a full term baby would. Don't turn a log into nightmare, however.
Wet diapers indicate baby is getting enough fluid, and BMs indicate baby is getting enough calories.
Experiment to see what works best for you. If Baby A has the left breast one feeding, give him the right breast for the next feeding. Or, if you are nursing one at a time, let him finish with the first breast, burp and change as needed, and then offer the second breast. Then give Baby B the second breast to start with. Switch breasts every day.