I have a fenced yard, too. I ran a fence down the middle of the yard to separate it in two. This might work for you. (I also have gates inside at doorways and a doggy door to the yard.)

I do think that both of your older dogs could easily become inside dogs. I have found that formerly-outside dogs almost housetrain themselves. As long as they already have a few reasonable manners, they can be taught house rules.

If Beulah is dominant, you should allow her to be boss of Tippy. Expect a few fights and don't interfere unless you see blood. Beulah will pin Tippy and look like she's going to kill Tippy. A couple of these episodes and Beulah will be confident that she is still the boss. Once Tippy accepts this fact, you shouldn't have any more fights. The hard part is letting them fight it out.

I brought a shelter dog into my small house and he became the dominant one. Both of my other dogs were smaller--Shih Tsu/Poodle & 25 lb Sheepdog--He was 55 lb shepherd mix. After a couple of dandy fights with the sheepdog, the shepherd felt in control and they lived together in relative harmony for 7 years.

I hope my long story will help