Breastfeeding twins questions

I’m only 27 weeks but already feel soo discouraged mostly from friends/ family comments saying I’ll learn for myself I won’t be able to do it. Over it but still have lots of concerns. Like how do you know when they’re done feeding and how do you keep track on how many oz they just gulped down? I’ve read your supposed to do 15 minutes on each breast for a full feeding but that doesn’t make sense to me. Is it ok to just keep the twins on the same breast for the entire feeding? And when are you supposed to pump to store? After each feeding? Lol sorry for so many questions obviously this is my first pregnancy and I really want to succeed in breast feeding. Also is it possible to just strictly pump and bottle feed breast milk to keep track of how many oz they’re drinking?