“That if any of the heirs of entail before mentioned, or their descendants, shall happen to succeed to the estates or titles of Marquis of Tweeddale, Hay of Drummelzier, Duke of Roxburgh, then and in that case, the right of my lands and others before mentioned in the person of such heir of entail, so succeeding to any of the foresaid other estates or titles, shall cease and terminate, and that from the Whitsunday or Martinmas next after he shall have so succeeded; or in his option, next after he shall have a second lawful son attained to the age of fourteen years, during which space I herewith dispense with the said heir of entail his using my surname and coat armorial; and the right of the lands and others foresaid shall fall and devolve