Just for reference purposes:Your father presumably gets an adult dependent allowance in respect of your mother, which is not much less than the pension your mother would get, if she qualified.
Something that could make a small difference is your father's other income. This adult dependant allowance would be taxed as father's income, and if he is using up his tax credits on other income the benefit they receive would be reduced.an adult dependent allowance in respect of your mother, which is not much less than the pension your mother would get, if she qualified