In your DF folder, there's a folder called "raw". Inside that folder, there's another one called "objects" with an assload of .txt files inside. Put the files there. I tend to make my mods so that you can just drop the files in and play, so you don't have to actually change any existing raws. (NOTE: I can't actually remember the names of the relevant folders without my DF directory in front of me. Yes, this is sad. No, you should not be surprised if I just unwittingly sent you on a goose chase.)
As long as you give credit, you can do anything you like with any of my mods. Print the raws on a wedding cake, if you like.
My Spawn already have their own entity file, though you could probably transplant the creature def into another without much trouble (I'm sorry if I misunderstood you here; it sounds like you have your own entity def that you want to use them with, but I'm a bit blurmy right now).
Out of curiosity, what's the difference between yours and mine?