Every single will has to go through some form of government process operated by the probate office. The reason for this is to ensure that there are no monies owed to government and no inheritance tax to pay.
Talk to the firm of solicitors, they may be willing to renounce their right in exchange for a fixed fee. Solicitors executor charges, from my experience are based on a fixed percentage of the value of the will, so if they don't renounce entirely, your taking on more of the work may not save you any money and may just save them work.
Thirdly its not up to the immediate family, although of course they want to maximise the inheritance and I can see why and in a way, agree with them, but its arguable that the deceased wanted to have solicitors as as one of the executors and that forms part of their wishes and should therefore be adhered to.