Hello :) I love the name of your fur babies! The thing with chihuahuas, or any small dog, is since they are so small their bladders and tummies are small as well. This means chihuahuas need to eat/drink more frequently and therefore got potty more often. Tippy and Babs can't hold it as long as your terriers did (you didn't say what kind, but I would guess they were bigger). I would designate a potty spot and put down some paper or pee pads so they can relieve themselves throughout the day. My chihuahua has a litter box in her crate and that works very well for us. Consistency and praise are key.
-Amanda-
