Hi Joy, how are the little ones doing? I think, it's normal the lil one finds it hard to latch on. She's so tiny. But don't worry. The most important thing is that she's healthy and keeps on suching. Hold on to her while she's sucking so she does not slide down the mummy's nipple. Is Peaches a first time mother? If she is, then it's normal her teats are smaller.
I think the lower teats are the easiest for the little ones to suckle. Don't worry about the size of Peaches' teats. Make sure the tummy of the lil one gets bigger each time she feeds. That's the safest way to know she's sucking.
You're doing a great job. Keep it up. Wish you and your lil ones the best.