You firstly need to ring Adult Social Services in your area - google for their number - and ask for a needs assessment for him. SS should then provide carers who can carry out personal care such as washing him.
If he is over state pension age, you should apply for Attendance Allowance on his behalf. He cannot have both PIP and AA, only one or the other.
https://www.gov.uk/attendance-allowance/eligibility
The forms are lengthy but it is well worth doing, so please don't be put off. As you have LPA you can fill in and sign the forms for him, you then send a certified copy of the LPA with the form.
You can use his AA for whatever you works best - you could for example use it to pay for a carer to come in to help him, if the care SS offer is not sufficient.