Co-executor won’t sign off on Estate value

[Trampas]

My brother, who is co-Executor of my late fathers will, won’t sign off on the Estate value, so we can move forward and gain probate. The Estate is under the Tax threshold, even with gifts over the past 7 years, but he is arguing that although he did previously agree to the gifts Dad made to his grandchildren, because I have more children they are unfair, and should go back in the pot to be split between the 2 of us. I disagree, as I gave the gifts £5k) each to the children, I don’t think he did - but he wants the extra £5k back in the pot. He won’t sign off, and refuses to get a solicitor. *Do we have a time limit to declare to HMRC, and to pay the Cash bequests to the Beneficiaries. We are almost not speaking now, so not sure what to do?*