I believe you are doing the right thing and at the right time. All kids are different so don't get scared by some of the other Mom's who might say that 17months is too young. Both my boys were completely potty trained right after they turned 2 and they are 4 and 6 and we have had no regression of any kind and when do you think I started talking to them like you are now? That's right, same age!
Here is what I have known to be true:
*Talking with them about the bathroom and what you do on the potty is the first step.
*There are quite a few steps :)
*When they begin to ask questions (even tho they might not be that verbal) or even say "potty" take them to the store and pick out a potty. I suggest the SOFT seats w/handles that go over the toilet and a step stool (kids like these and I NEVER wanted to clean out the small ones, yuk!)
*When you get home put it in the bathroom and ask them if they have to go potty. If they say "no", no biggie, say "okay" and leave it alone.
*Let them see you going potty and ask them again, every time. Same thing w/your response to "no" but if they say "yes" let them sit on it for awhile(1-3 minutes, I sang them songs to fill the time) and try. Usually it takes lots of trys before they actually go, so don't get discouraged! We gave high fives and said "good try"!
*When they do actually succeed in going potty, MAKE A BIG DEAL OUT OF IT! Big praise, clapping, telling everyone in the house/family, calling Auntie & grandma and yes, we did the potty signing..."U did pee-pee in the potty, pee-pee in the potty" but you do whatever u think your girls will like, we did dum-dum suckers w/our 1st but didn't need anything w/ our 2nd (like I said, all kids are different).
*When you notice they are getting really good at going when asked if they had to AND start waking up dry in the A.M. OR when they start asking you to go potty (we are in the beginning stage of this step w/my last baby) go to the store and let them pick out pretty panties and talk w/ them about getting to be done with diapers and be a big girl! Yeah! Talk w/ them for a few days, to get them used to the idea of being in underwear.
*Ask them in the morning when getting dressed if they want to wear panties and if they do, act excited and put them on and then be prepared to ask them @ every hour or so if they have to go and be prepared for accidents--IMO, this next part is IMPORTANT!--Put them in sweats or something that is easy for them to pull up and down AND DO NOT MAKE A BIG DEAL OUT OF IT IF THEY HAVE AN ACCIDENT and JUST CHANGE THEM RIGHT AWAY! I said "Uh-Oh! lets fix you up" and put on new undies...no biggie!
*When they ask to wear the panties, don't go back to diapers!
*Make sure you have the time because you want to allow yourself and them at least a few days, if not a week with continually asking them if they need to go.
*Accidents will happen, so be prepared...no biggie!
With my first 2, I didn't introduce the underwear until they were waking up dry in the mornings...made me think their bladders were strong enough to hold it, if they needed to. Also, I never did pull-ups. They just weren't necessary but if you do not have the desire or ability to be doing lots of laundry I can see the appeal...If you think you want to use them I would do night time only and regular underwear during the day.
Hope some of this helps. When you think your girls are ready, I say "just do it'!!! It will be okay and really, it isn't that scary! Promise.