AFAIK there are only these 3 tables to do the calculation. Read the few descriptive words on each to see which one to use: https://www.irahelp.com/printable/20...and-tax-tables
Uniform Lifetime Table is used for the original owner unless:
Spouse is >10 yrs younger. Then use Jt. Life table for more favorable terms.
Son is a contingent beneficiary so does not come into the calculation until he actually inherits. Spouse (once they inherit) can choose to make IRA their own (be owner) and use the Uniform Lifetime Table or choose to be a beneficiary and use the Single Life Table. They would probably only choose the latter if they were younger than 59.5 and needed to take distributions w/o penalty. Note that there is a difference in how spouses use Single LifeTable compared to non-spouses (see table description).