I've done reptile rescue for years. You have no idea the number of animals I've seen where a dog did something the owner never would have expected. I've heard "Ooooooh, it was totally out of the blue! Fluffy and Scales have been best friends since Fluffy was a puppy! I don't know why she did it!" Doesn't matter. Scales is missing his tail.
I'm totally sure you fully believe 100% that you know your babies. But so does mother nature. Deep down inside your babies, ESPECIALLY TERRIERS, is an instinct to kill. They are designed over centuries for that task. You can suppress that instinct with chew toys and exercise, but you can't erase it. It's there.
I've seen Iguanas with missing tails, I've seen mauled red ear sliders, I've seen a ball python bit in half coz they escaped and had an unscheduled meeting with a Labrador's jaw. EVERY... SINGLE... PERSON... said what you just said, and all of them lost a perfectly lovely reptile as well. So you can definitely keep your terriers with your tortoises. Dress them up. Put a bow on each, but please, if/hen something should happen, please don't call me or another reptile rescue to come salvage the mess.
My sister has been involved in turtle and tortoise rescue for abt 100 years...after I was medically retired from my job...she started having me care for some of her rescues...my first Gopherus agassizii...was named Mildred. She was 20 years old and had lived with her keeper and a dog. Mildred and the dog never had a bit of trouble until the day they did...the dog chewed off Mildred's right leg while the keepers were at work. Evidently he ate the leg as it was never found, also the stump had stopped bleeding probably because the dog licked it. The people dumped Mildred off at my sister's and kept the damn dog. So I took Mildred. She was regal, dignified and just a really nice tortoise...hey @Yvonne...I can't find a photo of Mildred...you have one?