Having this experience recently, my personal view is get a solicitor to do it all.
My Dad sorted my Nan's probate, which was incredibly simple, and even that took 9 months of stress.
My uncle is sorting his father's, and is finding it a nightmare, and until recently he was a probate solicitor!
In my case, we had excellent solicitors. I still had to do various bits of paperwork, and organise the sale of her house (all in the middle of Covid, and Mum lived the other end of the country) but it was money incredibly well spent. Didn't need to pay up front, just taken from the final inheritance.
I appreciate it won't be appropriate in all cases for a multitude of reasons, but it takes away a lot of stress. Trying to do something very technical, at a time when you're likely grieving, can add to the stress and lead to unintentional errors, as one PP has sadly experienced.
There is an Industry grouping called 'Solicitors for the Elderly'- worth getting one from that group to assist with any pre (eg LPA) or post death issues.