Newborn baby feeds for such a short time.

Hi, breastfeeding can feel uncertain, right, because you can't see exactly how much is actually going in! Maybe check how much she drinks from a bottle when you pump, just to reassure yourself? Otherwise, I'd suggest taking the little one to the health center to be weighed. If she's gaining weight, you're good to go. Then you've just got an easygoing aunt who's apparently sleepy.

A lactation consultant can help you figure out if everything is going well with feeding. You can also email your questions to La Leche League if I'm spelling that right. They tend to respond pretty quickly based on my experience, and you don't have to empty your bank account. Always handy.

In principle, it doesn't matter much, but I'd want to rule out subtle underfeeding. Maybe you can do a quick Google search on the symptoms to check? Then look at the number of wet and dirty diapers in a day; as long as she's peeing enough, you're fine, I think.

Try to trust each other as a couple. A baby basically regulates breastfeeding themselves; if there's not enough milk, they usually make that clear! I'd say try to enjoy it! Best wishes.

One baby drinks short but powerfully, and the other for longer periods but less powerfully. As long as your baby is gaining weight and seems content, everything's fine. It's indeed tricky that your breasts aren't transparent measuring cups so you can see how much comes out.
Pumping can give an indication, but keep in mind that no matter how well you pump, a baby who is latched on well and drinking well will always get more from your breast than what you can pump.