Firstly, if he's died without a will, the the succession act applies. Presuming his parents are also dead, then this money will be split evenly between nephews and nieces.
Yes, to fully access the funds you will likely need to go through the probate process as his bank accounts are >25k - this gives the right to both access the money and distribute it in accordance with the succession act, after expenses (e.g. funeral) are paid off his estate. As Sarenco says it's likely the bank will allow some of the funds can be accessed to pay off bills that need paying.
Task 1 is establishing the assets held - ie with which institutions, which account numbers and how much is in each - the bank can help your friend with this - they will have to prove their own identity and evidence of next of kin. Again it depends how orderly the uncle has left this information - some leave a nice list of a few accounts, and for some the next of kin has to be Sherlock Holmes.
This is needed to apply for probate, either with a solicitor, or it's possible for your friend to do the process (especially if the assets are very simple) - there's lots of threads in here about the pros and cons of doing it yourself.
After probate, they can access the funds, pay off anything that needs paying and distribute the remaining assets.