The solicitors are quite correct you cannot be paid under the terms of the charging clause if it’s the usual charging clause “any of my executors acting in a professional capacity” because you are no longer acting in a professional capacity.
In my opinion, this is not a secret trusts but is more likely to be promissory estoppel. He expressed the wish that you were to be remunerated but didn’t do anything about it it seems within the terms of his will.
The difficulty for you is that the potential value of your claim in promissory estoppel is probably going to be far less than the cost of bringing your claim and it could be risky if for any reason your claim failed.
Although any claim you bring may be under £10,000 (I don’t know how much time you have spent on this) and hence may be Small Claims Court, a claim for Promissory Estoppel would be part 8 proceedings and you would be at cost risk regardless of the amount involved.
I don’t know whether you are still involved with the administering of the estate could simply refuse to deal any longer and then the estate lawyers (I don’t know how they have become involved) would need to make an application to court to remove you. Of course, they get paid for that so they would probably be rubbing their hands.
You cannot force the 5 beneficiaries to pay you but they may be reluctant to litigate with you if there is a risk that they are going to have to pay money in the event that your claim is successful.
To my mind, ultimately, you were made a promise (that you would be paid) and you relied on that promise to your detriment (acted as executor) and hence, the estate is estopped from denying the promise and not honouring it.
Can I clarify anything for you?