Hi, J.. I'm a day care provider also and haven't tried potty training twins, though I've been through training more than one child at once. And the first thing I would say is embrace it! When more than one is training, it's more work (more trips to the bathroom, and some days I feel like I never leave the room), but it offers them both motivation to keep up with the other and have someone else to identify with. We have a small bathroom and though we bought a potty seat initially, I didn't like the way it seemed to hurt my son's bottom (he would stand up and have a ring around his bottom from the pressure of the seat) and it was a lot to have in the bathroom. So now we have a small stool and a soft seat that goes on top of the toilet, and that's worked out for us.
With needing a second toilet, we've been through that problem too. And really anticipating needs seems to be the answer. Early in training, try setting the timer to remember to go try, both at once. Then you have fewer emergency trips. And whenever one goes, encourage the other to try too, which ups their enthusiasm for doing it together as well as making it less likely that you'll have an emergency later. I also highly recommend "Toilet Training Without Tears," which advocates a number of training tools, but the one I find most useful is an "elimination chart." Write down (for each child) the times they go to the bathroom, what--if anything--happens, and any wet or dirty diapers with times. It helps you to see patterns in their elimination so you can anticipate needed trips, and you can see as the weeks go by that there has been progress, even when it feels like there isn't. When I was working with my oldest, I made several versions of this chart to carry us through the process, so PM me if you'd like me to email them to you; I'd be happy to.
Good luck!