Hi
Sorry for the delay. Was travelling today, but I've got home now. Here are some thoughts in response to the points you raise.
I've seen what others say on here. If I were in your shoes, personally I would try to get accommodation.
But the choice is yours, I respect that.
So if you plan to camp in winter near Fort William, here are my thoughts.
What sort of tent do you suggest?Tents tend to be divided into those for backpacking and those where you go (usually by car) to a campsite. The former are lightweight and designed to be moved about, the latter are heavier. A "Campsite tent" would be better for living in but if you need to move from place to place that would be a real problem.
I would advise looking at campsites first of all. Are there any that would allow you to stay "off season" for a nominal fee for a long period? If you can get some kind of arrangement with a campsite, then go for the "Campsite tent". Popular makes are Quechua (decathlon own brand), Vango and Coleman. Look on Ebay to see if you can get one second hand. You may get a better deal looking at the end of the summer season when people having finished using them and are selling them. Yo umight even get an end-of-range new one for a bargain price.
Are hand cranked chargers any good?I don't know, but there is an article here
https://trailandsummit.com/hand-crank-phone-chargers-do-they-actually-work/Is there any cheap places to stay you can recommend for is we need to get out the weather? That accept dogs and a cat?try these
http://fortwilliambackpackers.com/and
https://www.ben-nevis-inn.co.uk/accommodation/Any advice on the best type of clothing to keep us warm?First priority if you are camping is sleeping bags that are warm enough. Get foam camping mats to put under them, that helps a lot in terms of insulating from the cold ground. Even bin liners (under the foam mats) are a help.
You may find it cheaper and warmer to have 2 cheaper sleeping bags each, one inside the other, rather than higher spec more expensive bags.
The main principle to bear in mind with keeping warm is: use things that trap air which helps the insulation. Fleeces and a woollen base layer under a waterproof coat are the best combination. You can sometimes get warm gloves, hats etc in the "middle aisle" at Aldi or Lidl, but goods like that tend to be very seasonal. Look in Oct/Nov.
I hope that helps. Most of all I hope that you find a way to get a roof over your head, but if that is not possible then I hope that has been of some use.
Tim