You should apply for the citizenship certificate for your daughters at the London embassy, see instructions here:
http://www.cic.gc.ca/english/citizenship/proof-how.aspThe processing time is unfortunately well over a year. If you have tickets to go to Canada, you can ask for them to be expedited. Even if you don't have tickets, you could try it based on your concrete plans to move once your wife gets her PR. The sponsorship of your wife through the UK will most likely be faster that the citizenship certificates. The younger one can get a temporary passport even if the citizenship certificate is not ready. The older one could possibly get some type of letter or a travel document. Do they already have passports from some country?
When you arrive in Canada, depending on what province you will be moving to, you might have a 3 month wait for healthcare (Ontario, BC, Quebec and NB) in which case you should take out a 3 month emergency and accident (travel?) insurance before you move. If you move to some other province, you can, as a citizen and PR moving from overseas get instant health care. You can apply for SIN numbers and get them instantly but the SIN cards will take about 2 weeks by mail. The PR card will take around 6 weeks to arrive. Here is how you apply for child tax benefit:
http://www.cra-arc.gc.ca/bnfts/cctb/fq_qlfyng-eng.html#q8