DD1 dropped her sleep entirely at 20 months, so I won't even bother giving you the run down with her
DD2 was still having 2 sleeps at 14 months, I think it was around 16/17 months we dropped to one sleep. So instead of 2 x 2hr sleeps, she went to one 4 hour sleep.
But, seeing as she's sometimes up until 11pm at night, I would be lookig at 2 things:
1) what time does she wake up in the afternoon? Don't make it too late. I usually don't let DD2 sleep later than 3.30m (at the absolute latest)
2) dropping to one sleep. DD2 usually goes to sleep between 11-11:30 and will sleep for 3.5-4 hours.

When they're teething, yes, it is normal for sleep to be all over the place. Very common. You just have to go with the ride, and try and make it as comfortable as possible for her.

Sorry, not sure on number 3.