Situation: (uk location)

Parents divorced long time ago, Dad has a new wife (long time ago).  Dad is 2 decades older than my step mum so would likely die before step mum.  In his will i am a substitute executor of his entire estate.  My step mum is executor.  In step mum will i am executor of her estate.

I told my dad....if it was his intention (he says it is after both him and step mum die) to leave me his estate (money is largely his) i feared the step mum will could be changed for whatever reason if he was to die first. -  which it can right?

I asked for stipulations to be made so that after his death the step mum cannot radically alter her will. Do such stipulations even exist ?