Hi K.
Hey don't get yourself nuts! You do what YOU think is right for your babies...never mind what you read and what your babies are "supposed to do".....PLEEEZ the books and "the experts" can make your head spin.
My daughter is 14 1/2 months and she still takes bottles.
I come from a family that keeps babies on bottles until 18 months or longer if needed.
I had her on soy since she way 4 weeks old Health issues kept me from breast feeding her, but when I did in the very beginning, it was the most wonderful experience I have ever had. I put her on Good Start since she was very colicy and the Good Start has predigested protiens so the colic got better right away. I have her on the Good Start Soy stage 2 now. I do not have to worry if she is getting the proper nutrients from her food and I do not have to suppliment vitamins. She gets 2 to 3 formula bottles, a bottle of whole milk and juice too. I was nervous about giving her milk, but I just did it gradually. I actually gave her some Yo-Baby yogurt first and once I saw that she did fine, I gave an ounce of whole milk and she loved it. No tummy upset either.
I found great advice about changing formulas from the formula companies themselves. I first used Similac from the hospital, then gave her their soy based for the colic, then I went to Good Start, both formula companies were extremely helpful. They know their products best and can help you the most. I agree that formula is way too expensive, but I only have one baby...you have 2. I know it can be tough sometimes and I think it is outrageous that basic food for a baby can be so expensive!
I do know that the people at Carnation told me that the protein from milk is a smaller protein than a soy protein. When our babies are infants, that is when they really get into trouble. When they are bigger (one year), they usually don't have issues with changes except if they have allergies to what you are giving them. Try it slowly, that's the best advice.