You can get all the information on gov.uk.
You can give away what you like, but these are possible repercussions:
Inheritance tax - as eddiecat78 says. You may not be liable for inheritance tax anyway. We have done this, and accepted that if we both die in the next 7 years, then a small amount of tax may be due on our estate. Martin Lewis over at MSE explains this well.
Liability for care costs is less straightforward. You cannot give away money or your house, and then claim for the Local Authority to pay your care costs. However, you can give away money as you are intending, at a point where you are in reasonable health, and with no expectation of needing care in the near future. If something catastrophic & unexpected happened, then you could, if needed, still claim for care costs. Again, you may not be eligible for local authority funding anyway, so it would have no effect.
Very generous of you - they are fortunate