Having gone through all the paperwork recently for mother in law I would suggest:
Get financial/legal power of attourney for him. If he agrees this can be enacted immediately (well it takes about 2 months to come through). This means that you can make financial legal decisions on his behalf - whether or not he at the capacity to do so. (For those queirying Financial / legal POA needs to be set up whilst capable and can be set up either as for use asap or for use only when incapable, Health POA however needs to be signed whilst capable but cannot be registered until incapable.)
You say he needs nursing care - Has he been assessed for this? If not ask for an assessment. Is he currently in hospital - if he is then they can organise one - of not then his GP can refer to social service for assessment (or I believe you can.) Is his condition long term but not life threatening eg dementia, or is it medically life limiting e.g. cancer? The answer to this will make a significant different to how he is treated. If he has medical needs and is expected not to live for more than 3-6 months then his care will likely be NHS funded. This is difficult to get but seems considerabley more likely if he is in hospital and the hospital need his bed!!
If he is at home currently it is likely that they will want to keep him there unless assessments show that he really cant manage. You need to be very careful about assessments at home as they will ask what you are going to do to support him. Unless you want to become his fulltime carer then I would advise you say that you cannot do anything - cite work, distance, kids, anything you like - but make sure you tell those doing the assessment that you cannot help. That way he will get what care they can offer and anything you can do will be extra - not that the system is reliant on you to care for him.
In terms of sorting out his benefits/pension any care assessment will ask what he has coming in anyway so it is going to come to a head at some point. I would probably say you do not know why he doesnt have a pension etc as the info you have seems quite vague and suggest that they look into it. He will likely be entitled to attendance allowance in addition to anything else he gets unless he receives fully funded nursing home care.
At the end of the day if he does not qualify for NHS funded care, and does not have the funds to fund his own care then the social services will fund his care. They will prefer to keep him in his own home for as long as possible, and at the point he needs to be in a nursing home then they will place him where they consider the best value for money - you will likely get little say in this although you will probably be able to influence the area in which his is placed so in the district of his current home / you home if you are the only relatives - but no more than that. They will then take all pensions/income etc other than a small budget - something like £10 a week - which you will then be able to use for extras such as getting his hair cut.
A word of warning: once you open this hornets nest you are going to end up spending ALOT of time sorting stuff out for him. You need to consider whether you have the time before you do this as it is consuming (- and will need to all be done in normal working hours 9-5 mon-fri!).
If he has any cash available now I would also get him to consider setting up a funeral plan - otherwise you may find that there is no money left over to pay for that. (£1500-£2000 minimum I think).
Good Luck!!