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If your husband is British he is your sponsor and should be the one receiving a carers allowance to be exempt not you the spouse.
First of all are you married to a British citizen? or some one with ILR?
Your question said you are awaiting to apply for a spouse visa. You are not applying for a spouse visa it is your wife applying for a spouse visa. So I read your question correctly. So we are clear now that you are the sponsor of your wife's application for a spouse visa.
Please clarify how someone receiving a carers allowance can also be a carer for someone else. It does not make sense because someone receiving a carers allowance needs care themselves and if they need care themselves how can they then claim they are capable of caring for someone else? The Home Office will not understand this scenario, I certainly don't and this is a very unusual situation. It needs clarification before I can attempt to answer your question. Do you have any evidence clearly confirming you are receiving a carer's allowance? If this scenario is commonplace in Scotland as you stated Scots law then the local authority will need to clarify this to be normal practice before any exemption can be considered on its merits. It s certainly not a scenario I have come across in my years of practice.
Ok all you need is evidence that you receive a carers allowance to be exempt from the financial requirement. If you have a letter from DWP confirming this then you would be exempt. Dont complicate issues with ESA as income from ESA does not count towards the financial requirement. The fact that you are entitled to carer's allowance and you receive carer's allowance to look after your dad and you have the evidence from DWP are sufficient to exempt you.