Bishops Children are open centered dahlias from the dahlia Bishop of Llandaff. No dahlias come back true to the parents from seed so you are likely to get a mixture of colors if you try to keep seed. The blooms from the tubers you get from your Bishop's Children will have the same color as their parent. These open centered dahlias are the easiest to get seed from & if you're not fussy & looking for good show quality dahlias they can be fun to experiment with.
As for keeping them growing over the winter- they need a lot of light unless you just cut them back & store them in the container. They will get really leggy if you don't have lots of light. See other posts from the last few days on this forum about some people trying to grow them inside over the winter.