Hi Lynne.
Sorry that you have been having problems with these sores on your feet and hands.
As a Podiatrist in a previous life (long story!) I would suggest that you see your GP ASAP about this blister on your heel - it's probably nothing but the last thing you want over the holidays is for it to get worse or get an infection in it.
I would also suggest that you see a Podiatrist that could dress this blister appropriately for you. If you are registered with an NHS Podiatrist already, they will have an 'emergency' number that you can phone to be seen very soon. If you aren't already registered with the Podiatry team your GP will be able to refer you. Most NHS Podiatry teams will also have 'emergency contingencies' to cover the holidays.
Unfortunately, with methotrexate, delayed healing can be a side-effect - I know from personal experience.
The only other bit of advice that I can give you is to keep UNBROKEN skin moisturised. As JulieM suggested, you can get huge tubs of unperfumed aqueous creams either on prescription or direct from the chemist.
Hope this helps a bit
Take care.
Sara x