two new shih tzus

Question
My grandmother and I "adopted" two shih tzu dogs from a woman that couldn't take care of them any more.  To make a long story short, we are on vacation and were looking for the local humane society to adopt an animal because my cat had just passed away.  The woman offered us her dogs and we picked them up a few days later.  The problem is feeding them.  I know what the portions say on the bag and my grandmother has had experience with many other dogs, she is the one who is feeding them.  The male is larger, about 20 lbs.. and is long and thin.  The small female is (supposed to be) about 12 lbs. but she was pleasantly plump when we got her, not fat, but now that we've fed her she is bordering obese.  I am aware that these dogs are supposed to have allergies, but other than what I have read from various sources, mainly wikipedia, I don't know much about allergies from food and I doubt our dogs have them.  The truth is the woman was feeding them generic store brand dog food that had the animals fat, and meat-by-products in them.  The little dog scratches all the time, and the bigger dog has tiny skin flakes in his fur.  I know washing them often will help, they don't like it but we do it anyhow.  The groomer told us to use a soapless shampoo that was non toxic.  I want to know if anything might help their skin/coat problems.  I am also wondering what brand of dog food to feed them and I am hoping to find one they will like to eat.  We think they might have been fed table scraps.  They have been spoiled with chicken or beef broth on their food and they are being fed Dick Van Patten's Allergy free lamb & rice and the organic with chicken.  They won't eat it dry.  They both have puppy cuts and are about 1 1/2 yrs in age; they are both spayed/neutered.  Also, the woman kept them in a large cage all the time while she was at work and they aren't firmly aware of house breaking rules.  Their cage was badly assembled, they can escape from it, and I had to tape the top on. Now it is closed with small bungee cords at night.  We've started them on different ideas for housebreaking, mainly taking them out every 3-hrs, sometimes only 2 during the first weeks.  They don't seem to be having many accidents this past week but it has been a reoccurring problem and they don't know any better.  I've corrected them right after the accidents and taken them to puppy pads to show them better.  They are fast learners but I am worried the problem might persist when we take them to our home in Maryland.  We have a yard there but the house is large and we are not sure what to do with them once we are there, obviously certain rooms with be gated. The male whines until we can't stand it if we lock him up where he can't see us and he is a pain and very insecure in the car.  They do sleep in the crate at night and we let them out one last time at 10 before bedtime.    We have bought a large new crate for them that is well constructed and they have a large carrier/plastic crate for the car that fits both of them.  We have a two day trip in the car from Florida to Maryland.  Any thoughts on how to solve our problems or help adjust the dogs to their new home when we return to Maryland?

Answer
How much to feed is one of the easier parts of your question.  Your dog definitely should be narrower at the waist than the hips and chest. You should be able to easily feel the ribs, but not see them. Each dog is different. Standard recommendations are a good place to start, but each dog must have its food and exercise adjusted to its individual needs. Here is a link to a good illustrated guide, http://www.longliveyourdog.com/twoplus/RateYourDog.aspx  Among the problems over feeding can cause is skin problems.

The type of chow is a subject that draws more heat then light.  There are no studies available to the public comparing how dogs do eating different diets.  Nearly everything you see is based on speculation.  What you read on Wikipedia may have been posted by somebody selling a certain brand of chow.  The only information I trust is what I have seen with the service dog schools.  Long, active, healthy lives is a major goal.  I know they have looked at different diets, and they are feeding common brands, Iams, Pro Plan, Science, etc.  I would pick one type of food and stick with it for at least a month.  The fewer different things they are eating, the less likely to have a food allergy.  

I disagree with the baths.  Feed a decent chow and as little else as possible, seldom if ever bathe the dog, and brush it daily with a soft bristled brush. You might add a teaspoon a day of liquid cooking oil to its food.

Thin them out, stick to one chow, skip the baths, and brush them daily.  See how it goes.