Having acted as executor for a complex family estate I confirm that the whole business can be a total minefield with unexpected effects unless the will is very carefully written. Percentages, unless they are equal shares to relatives can give the executor a real headache and percentages to charities can be an open invitation to problems as mentioned above.
As well as financial assets, something else to remember is the personal effects of the deceased. It is common practice for beneficiaries to be able to express an interest in items of sentimental or practical value with those not chosen being sold off at auction. This can work if everyone is on good terms but not so much if two beneficiaries want the same item or say, the daughter wants all her Mum's valuable jewellery which makes up a disproportionate value of the personal effects. It an be a good idea for all the effects and furniture etc.to be formally valued then if one beneficiary chooses items of greater value than the others then they get a smaller share of the proceeds of the remaining stuff that goes to auction. Some of this, such as jewellery, can of course be itemised in the will and often is but can distort the overall shareout if there are several beneficiaries.
I strongly recommend getting a will drawn up by a competent professional who can explain unintended consequences, don't use unqualified will writers or, Heaven forbid, the pro formas from W.H.Smith. That way disaster lies!
NEVER appoint a bank as Executor as they will usually charge on a percentage basis plus expenses and will leave a huge hole in the amount left for distribution.
A solicitor can be better but will still be expensive
Both banks and solicitors work at their own pace which can be frustratingly leisurely, especially if there is a house to be sold. They also depend on the family to provide them with all the information and documents they need so those left behind still have a job and a half in assembling all the paperwork anyway.
Best of all, if you have a trusted family member who is savvy with paperwork and is willing to act as executor then appoint them, preferably with a backup in case they pre decease you. That way they retain control of the process and the beneficiaries (of whom they may be one) will bless you. Dealing with most estates is not difficult, you just have to be methodical and willing to read up on the rules. There is plenty of advice out there. Some matters will need professional input but the executor can employ solicitors and accountants as and when required which keeps fees under control.
In my case I reckon that doing the job myself must have saved at least £10k-£15k in 'professiona'l fees and 9-12 months in completing the process.
Colin