Hugs mate, sleep issues are the absolute pits!

1). Only speaking from my experience, we cut back Moo's day sleeps around 12 months. He was only having about 10 mins in the arvo and really seemed to need his morning nap. If he needs an arvo nap, by all means he can have one. But if it's after 3:30pm I stretch him out and put him to bed a little earlier in the evening. I haven't noticed a difference in him sleeping better if he has one sleep compared to two, but he is difficult to settle if he has a later nap.
2). I think it is normal. Moo started walking around 12 months and now he is getting more teeth. I do notice his sleeps go up the creek when he's reaching milestones and becoming more independant!
3). Sorry, no advice there. I have the same problem! Moo will not go to bed when anyone is here, including the airconditioner bloke we had around recently lol!

Hope I was of some help!