The American Girl Doll was easier to detangle (and now I understand why we spent a bazillion dollars more for her than the imitation)- there was a better quality to the hair among other things.
I googled detangling doll hair and found this. The lady who runs the site had some ideas. So first I took the doll who was worse- can you guess which one that was??? And got a cup of hot water and a brush. She recommends a wig brush but seeing as how I started this before reading and didn't have one of those, I washed a regular hair brush. I brushed through the tangles as best as I could.
Then I noticed it was still frizzy and looked through the site (which by the way has amazing tips on doing doll hair and even how to re-wig it). I saw that she recommended a "downy dip" well I didn't have downy liquid fabric softener. I had dryer sheets!! (darn I forgot to take a pic of this step) I put the sheets in bowls of water and let the dolls hair soak all day. I set the dolls in the window when I was done and it worked pretty well. When their hair was dry I brushed through.
They are not perfect, but better than before and am seriously considering re-wigging the imitation doll because of the quality. But I will probably just bite the bullet and buy an American Girl Doll for my younger daughter.