I would not use additional batting. The extra weight from that could make it hard for some to snuggle up with. Remember, when dressing for the cold, use layers. Several thinner layers of clothing works better than one bulky layer.
When you are sewing your top to the fleece, the fleece should be on bottom to allow the dogs to take up the slack. Fleece is forgiving and, I would not quilt these either. Use yarn or embroidery floss to tie at 6" intervals.
Your efforts are admirable, but remember, that unless you have an unlimited budget, many of these blankets will be lost, stolen or "misplaced". Do not spend your hours working on a project for "that dear person", because it is sad, but likely that it will become a ward of the facility anyhow.