Any plans for a pivot to a second career: horse boarding, earthmoving business...?
There is a lot of incoming money that's not accounted for in the current spending. There is 74K of income, and $6859 of Annuity money coming in, but none of it being saved. Unless it's paying off a debt, it's being spent somewhere.
I don't see any horse-related expenses: Vet bills, food, farrier bills, grooming. Boarding -are they on your parents' property? If so, Barn repairs, bedding costs. If not, boarding costs.
Without detailed cost information, or a knowledge of what expenses are going away, I'd assume your parents are spending all $80,859 that's coming in.
If they want to continue spending $80k in retirement, it looks like they are $52k short. At a 4% withdrawal, that would require $1.3M.
But,
There is no need for their expenses to stay fixed at such a high rate - Can the horse situation be changed, where they board horses for other people instead of owning their own?