Suggestion for the Disney doll hair. (Note I would NOT use this method on the AG doll as the hair on the AG is different)
1) Never use a brush on a doll that has been used on a human. (Human hair has oils that can really mess up a doll's hair)
2)I use a small dog brush(wire brush) (similar to the AG hairbrush)
3)I use a thick conditioner (usually VO5).
Remove the dolls clothes and cover any fabric body parts by tying in a plastic bag.
Submerge the doll's hair in a bowl of cool water.
Make sure all of the hair is wet.
"Glop" the conditioner on the hair and work your fingers thru as many tangles as you can.
Don't pull the hair. (The hair is most likely rooted and will come out if pulled). If you can't get all the tangles out, add (thick) conditioner right to the tangle and "massage gently" until the tangle falls out.
Rinse the hair to remove ALL conditioner.
Pat the hair dry with a towel.
Do NOT RUB!!! (It will tangle again) and DO NOT use a hairdryer.
GENTLY comb your fingers thru the hair while it is wet.
Once you can get your fingers thru the hair you can then use the brush. Start at the top and brush down , use small strokes. If some tangles remain you can lighty spray some tangle remover-I would not use too much on the Disney doll.
Once you have brushed out all the tangles, you may have to trim some "bad ends".
Let the hair (air) dry completely.
Your "baby" should be having a much better hair day.
This method has worked for me on dolls with rooted hair. I have even untangled Barbies hair this way.
It is important to note Do NOT use heat on these dolls. The hair can melt.
Hope this helps. If you have any questions or need addition help please let me know.