How much to feed baby?

Mo

My twins are 5.5 months old, and I’m starting to realize I may be under feeding them. They used to eat every 3 hours but now it seems they are always hungry after 1.5 - 2hours and we have only been feeding them 4oz(and one 5oz bottle in the morning).

When I looked online it says by their age they should be eating 6-8oz? Does that sound right? I feel terrible I didn’t realize my babies were still hungry, sooner.