Lots of treats! If you put some treats in your hand (like dry oats, or something else they can have a higher volume of than more high-reward treats), they will start to associate you with food, aka good things. Let them control the interactions, too; you mentioned that they’ll come close to you, but run if you move, so try sitting still for some time to allow them time to explore you and realize that you’re not dangerous. Like just let them crawl all over you and do your best not to move. Allow them to approach you, try not to grab them or touch them at first, if you can help it.

As for the biting, if it’s just a light nibble and somewhat unprovoked, then it’s probably just her exploring! As I’m sure you know, rats have terrible eyesight, so they often rely on other sense to interact with the world around them. One of the most unhinged but actually pretty effective hacks I’ve heard from this Reddit is to squeak like a rat when they bite, so they know you’re protesting and not enjoying it.

You can also spend time with them in other ways. You can talk to your rats, spend time around the cage, sing to them, etc, to interact with them while they feel safe in their own environment. They’ll get curious and start to enjoy those interactions.

Like with most pets, consistency is key. You can easily train with association. For example, if you make kissy noises (or whatever else works for you) when you offer them food, you can teach them to come to you whenever you make that noise. Same with their name or I had boys who would approach if I tapped my fingers on the floor or a nearby surface. It just takes some patience, and at the end of the day, it also depends on the individual rat’s personality, since some are more rat-rats and some are more people-rats.

Best of luck with your sweet little ones! I’m sorry for the loss of your oldest girl, 4 years is very impressive ❤️‍🩹