Mine both had dentals and they were fine. Sammy had terrible breath and actually she needed an extraction and that's probably why. Npw their breath is MUCH better. I do brush like 3 times a week and the vet said it helps but they still need dentals because it gets under the gums and they get x-rays and all that fun stuff. Yorkies have terrible teeth to begin with. Hootie & Hobbs will be fine.
P.S. Sammy has been under 3 times now and she handles it really well. Loki has been under twice. Just have blood work done to make sure kidney/liver function is OK. If there is a problem your vet won't put them under.