Looking at this product for Rottweiler puppy that will be spayed Dec 8th. Have an 1 yr old Rott big brother - will this help prevent him from licking her incision?

Absolutely will help a dog that is getting spayed.  The dog onesie was invented by a vet tech for this exact reason.
Puupies are already traumatized - the cone was not working- the softness and fit of the dog post surgery garment soothes the puppy and protects the stitches

My dog's measurements do not fall into your sizing chart. He is a small 1 one year old terrier mix. Neck: 9 inches, Chest: 13 inches, Length: 15 inches. I saw some reviews sayingthe garment was not long enough, and I don't want it to be too big either. Suggestions?

As you can imagine, dogs can be tricky to fit because of the variance in sizes.  We'd recommend you buy the one that gives your dog the coverage in the area you want to protect (i.e: Covers stomach after spaying, covers the tail, etc) . Then perhaps you can take the Tulane's Closet Post Surgery Onesie to a seamstress to make a dart to adjust the  protective garment.

Have A 70 lb RETRIEVER WHO HAS A CYSTOTOMY TUBE IN HIS BLADDER( right behind his thing) HE PULLED OUT. THINK THIS WOULD PREVENT THAT?

The Tulanes Closet Onesie has double padding (soft terry cloth) under the dog's stomach.
This makes it perfect for dog neutering or spaying recovery.  It is secured with a series of snaps, so you can secure it, or open it up when your dog needs to do his business.