Is my new BP underweight?

[200xth]

Well I got them a month ago from a guy who couldn't keep them anymore do to certain circumstances. He fed them an adult mouse once every two weeks. I don't think that it was adequate. I know you should feed them more often than that. But that was out of my control.
I will feed them an adult mouse every week for now and see how they do.

At 161g and 204g They have already outgrown adult mice (unless you're talking about the jumbo retired breeders that are usually around 40g).

If you have some rat pups you may want to try switching them to rats. As your snakes grow (and they will grow quickly once they are fed regularly), you'll be able to increase the size of the rat rather than feed multiple mice, which keeps things a bit easier. They may not switch to rats, but most likely they will so you may want to try it.