As Ellie has said, your Dad may be entitled to Attendance Allowance, at the lower rate if not the higher. It would also be worthwhile making an application for Pension Credit.
Does your Dad have carers coming in? If so, it may be that the local authority can do a financial assessment and part fund the care?
Do they own their property? Might an equity release scheme be an option?
Are they in debt? Credit cards etc, maybe they could see an insolvency practitioner to try and reduce their monthly repayments, maybe through an IVA?
Does your Mum pay income tax on her wages? It may be that she is entitled to a refund from HMRC?
The direct gov website has lots of information on it and links to all the forms you can download to make the claims.