Your father cannot give you money for you to pay for his care. Well he can, but you cannot claim tax relief on it.
If you pay for your father's care without being reimbursed, then you will get tax relief.
If you pay for your father's care instead of him, his estate will have more in it when he dies.
And so you and your siblings will benefit.
Any arrangement to settle this between yourselves so that you would get tax relief while not really paying for his care would be tax evasion.