We do have Continuing Power of Attorneys in Scotland, Welfare Guardianship/Powers also or a combination of both.
And of course receipts/accounts should be kept, for everything, as if they or you did or do go in the future, for the process, how will anyone know who can be trusted, or indeed capable of looking after that person and their finances.
It may be that you need to appear in front of a sheriff, and have paperwork signed by medical professionals, and of course have a papertrail/history.
Best checking out here for further information:
Office of the Public Guardian (Scotland) - What we Do - Power of Attorney Section
As to him contributing, as they were responsible for him, they would most probably been best to use his money to look after him/his needs, rather than what sounds like you're saying and charging for bed/lodging, etc..
The OPG will investigate reports of any mis-handling, or queries, and they can be contacted for more information at the above site.