To review, the earlier statement was:
To which my response was in the scenario where their client passed away a prudent and reasonable professional would write to the execs having been notified that the family did not have details. So therefore they could "unilaterally act".
It's hard to believe that an estate could end up mouldering for years, or a family end up applying for probate under intestacy rules, when a valid will is sitting in a Solicitors safe, but said Solicitors sit on their hands saying they are not allowed to contact executors.
You have strayed way off course here.
The OP’s issue was to do with another executor acting unilaterally to their exclusion. It has been pointed out that this is lawful, indeed envisaged and permitted by the Succession Acts, and that the Solicitor acting for the appointed executor has acted entirely appropriately.
You have brought into the conversation an entirely new issue which has to do with the custody of wills to which completely different legal considerations apply. The law here is per @jpd’s post.
However, a Solicitor who is the custodian of a will, whilst under no obligation to do so, may well think it prudent and reasonable to notify the executors. Many do, once they become aware of a death.
That said, Solicitors do not necessarily peruse the death notices pages daily just in case a client or former client may have died. Usually it’s the beneficiaries or executors who will be proactive and contact the solicitor to establish whether a will exists.
Some wills do end up mouldering for years because either the Solicitor isn’t aware of a death or the beneficiaries aren’t aware of who the testator’s solicitors are who might be in possession of a will.
To bring matters back on topic, where a Solicitor is instructed in the context of the administration of an estate by an executor, he must act in accordance with instructions. If the instructions are not to contact named Executor B, then he must abide by that. Or if the Solicitor thinks Executor B ought to be contacted, he must seek instruction from Executor A and act accordingly.