My daughter, and much more recently her son, both trained in a week or two (both at around 2 1/2 years). They were both ready, not only physically able to recognize and respond to urges, but also emotionally mature enough to carry it through. When they are really ready, kids are generally quite proud of themselves when they get the system figured out. Much like speech or walking.
I've known of a quite a few kids training between 18 months and 2 years, but it seldom seems to be permanent. If the children are not able to maintain interest and regress, it's probably because they are just not there emotionally yet. A pretty high level of commitment is needed.
I never gave my daughter more than a big smile and congratulations; no prizes, and she was just delighted with her new-found maturity. My grandson got a few prizes on a sticker chart, but he lost interest in those after only a couple of weeks. He was just ready, chart or no chart.
Pooping is a separate step for lots of kids. I think it just feels very different to poop on the potty, and the sensations seem to frighten some children. You can google this for lots of suggestions.
Good luck to you both!