this might be useful
Who can inherit if there is no will – the rules of intestacy - Citizens Advice
It will be a while before its sorted though so alot depends on how long the tenancy is for. As its not the residential property (an asset held for other purposes) it forms part of his estate and the law will dictate what happens to it or the value of it. The first port of call is to apply for letters of administration and if his wife is deemed not competent this could be done by his brother or by his children (often depends on who gets in first and the courts decision). This appoints the Executor or Administrator of the will who then applies the law to distribute the estate. They have to find out about all his assets and debts and pay off anything owing including the funeral from the estate, then when you know the value its sent to the Court of Probate for them to agree the appt. Any inheritance tax is payable at this point, you may have to negotiate this with HMRC if there is no cash in the estate to meet this and for e.g. a house needs selling.
Whilst all this is going on and it can take months, rent is still payable (to the estate) and any maintenance on the property should be maintained also by the estate (certainly the deceased's share of it).
Also you need to be aware if any fees need to be paid for your relative's wife it may be worth making sure money is in her name now rather than leaving it where it is as it could be tied up for a while - it need only be in an account in joint names as that would automatically become the wifes property on his death as I understand it.
If it is your father or step parent and all his children are in agreement its worth considering which accounts money is in and talking to your parent about it. I would document what you do though so that you are covered if things go wrong for any reason.
Its really worth researching what to do when someone dies and making a list of what order to do things so you don't get caught out e.g. how will funeral be paid for and from where, banks can release monies to funeral directors directly but only if there is money in the account. Everyone requires original death certificate and copies of the letters of Administration (or probate and the will) so doing things in the right order makes things go more smoothly - so hit the big amounts first to release monies to the estate, it is worth opening a separate bank account for all this in and out of money if you do the administration yourself, keeps it all separate from your own money and helps you keep account of distribution etc - open and transparent to others
Sure you will pick lots of other things up. The .gov website is also excellent for walking you through things