Great to hear that your wife and her daughter have received their UK settlement visas.
As you say, there are certainly lots of things to sort out and I'm sure other members of the forum will add to this but I'll add my own experiences thus far.
My wife arrived here in London in mid-May. Her spouse settlement visa does not allow her to access public funds such as JSA etc. but she is fully entitled to work in the UK and to make use of the NHS.
One annoying downside is that my wife cannot access free TESOL English courses at our local college in Camden until she has been in the UK for one year on her spouse settlement visa. Until then she will pay fees at the "overseas" student rate. This seems to be down to the funding rules for publicly funded colleges.
As your wife's daughter will be here in the UK on a settlement visa and as she is not yet 18, and as yor local Sixth Form college has rightly confirmed, she is entitled to state funded education (anyone born on or after 1 September 1997 must remain in education or recognised training until their 18th birthday).
The first things that I did were:
1. Get my wife's name on the Council Tax bill. I cannot stress how useful this has been as it's a recognised official proof of address which is needed to access so many different services;
2. Get a National Insurance number. I 'phoned the National Insurance helpline and explained her status in the UK. The DWP sent a form and covering letter explaining which parts to complete/ignore along with a prepaid envelope. I completed the form with my wife which we sent back to the DWP with the requested photocopies of her Thai passport biometric details page and UK visa. The NI number was issued in the post within 10 days;
3. Use the Council Tax Bill as proof of address to open a bank account - I bank with Nationwide and they couldn't have been more helpful. My wife had a standard current account opened for her on the spot and her Visa ATM/debit card arrived four days later;
4. Use the Council Tax Bill as proof of address to register your wife and her daughter with your GP. My local practice here in north London were excellent, and my wife was able to get an appointment within five days. Her NHS number came by post just two weeks later;
5. Get a SIM card;
6. Get in some Thai food supplies "for a taste of home". We're lucky living in London as there are plenty of Asian and Thai supermarkets selling Thai foodstuffs but she also brought a lot of ingredients with her (mainly the ultra hot chilliis and various rather pungent smelling ones);
7. Get a local public transport map/travelcard.
My wife also visited the Kapook (Thai money transfer) office near King's Cross to open an account to allow her to send money home to Korat. They needed proof of address (yes, that Council Tax bill did the trick yet again) and her passport.
My wife found a part time job very quickly and is now very independent in travelling around London by bus, tube and train by herself. Her employers checked her employment status and were pleased that she had been issued with a National Insurance number so quickly.
Regarding her current status and the future journey to UK citizenship, a major difference for us would be that UK citizenship will make travel to the Schengen area and beyond so much easier. UK citizenship also brings with it the right to vote, the right to work without restriction in other EU member states and to be called up for jury service.
For me, it's still a learning experience but a fun one!