I would also recommend leaving it until a few months after the arrival of DC2.
DD1 was 2.3 yo when DD2 arrived 5 weeks early. I am pretty sure she was ready for potty training already and had been 'practising' sitting on the potty for months.
I was not ready to train her whilst pregnant.
DD2 was in NICU and then I was not ready to train DD1 whilst DD2 was so tiny.
We then went on holiday to Holland when DD2 was 5 mo so postponed training until we came home as I did not want to have to find public toilets in a foreign country.
We arrived home on May 14 and DD2 started pre-school on the 18th. We started potty training on the 15, she went to pre-school in pull-ups (was only doing 2.5 hrs at a time) for the first week.
From week 2 she was in pants full time. Happy to pee and poo on potty. Last accident happened during week 3 - very little notice of when she needed to go and we carried a potty with us in the car!
By the end of the month she was dry and clean - day and night - and we have never looked back.
I am glad that I left it as long as I did even though she was ready before then. When I was ready she was able to get to grips with the whole thing and has been taking herself to the toilet at home, at pre-school and at the childminders with no fuss for months now.
You all need to be ready.