Welcome to YorkieTalk.
Is Hunter neutered? If he isn't, marking is always going to be a problem.
Is Abby spayed? If your dogs are unaltered, that may be a large part of the behavior problems.
Although my boys have been neutered, my younger one loves wrestling and he goes after his big brother a lot. They play bite each other. The good news is that the wrestling and play-biting is decreasing as the younger boy matures. Make sure Abby knows bite inhibition:
http://www.yorkietalk.com/forums/tra...nhibition.html
For potty training, I would limit Abby's freedom in your home. Keep her confined to a small area where you can supervise her or clean easily if you have to leave her alone and she has an accident. Continue taking her outside frequently (after meals, when she wakes from a nap, after playtime) and keep her out until she potties. When she does things right, praise her profusely and give her a small treat. Really let her know that you are happy. Don't ever stop giving her praise for doing things right.
Walking, instead of hanging out in the yard, also helps speed the process, especially for pooping.
Make sure you thoroughly clean the accident spots inside with an enzyme cleaner to eliminate the scent and discourage her from returning to the spot.
Hope some of this helps.