Keep it simple.
Here's a very rough draft for you (although it's nearly of a quarter of a century since I did this for a living):
"This is the last will and testament of me, Jourdain Two, of 23 Acacia Avenue, Sometown in the County of Hereshire. I hereby revoke all previous wills and testaments.
I desire that my body be cremated, with a Humanist service.
I appoint Fred Smith of The Larches, Uptown Road, Blogsville, in the County of Thereshire and Freda Smith of the same address as executors of my will. Should either of my executors pre-decease me, or otherwise be unable or unwilling to act as executor, I appoint the other named person to act as sole executor. Should both of these named persons be unable or unwilling to act as executors, I appoint Martha Bloggs, of 14 Hill Street, Little Hamlet, in the County of
I give the whole of my estate to my husband, Jordy Two, subject to the following proviso:
If Jordy Two shall pre-decease me, or fail to survive me for a period of thirty days, . . . [then set out your wishes, ensuring that 'the daughter-in-law who never was' gets mentioned but that the people you can't stand don't ]
Signed by me, Jourdain Two, in the presence of the witnesses who have signed below, this third day of October in the year two thousand and nineteen"
With regard to your statement that "he wants to help the lady who should have been his daughter-in-law, but has no legal entitlement", point out to your husband that he CAN'T do that UNLESS he writes a will.