Core Capital calculation using mortality tables

How can you adjust the core capital calculation for the capital gains tax that will be owed as someone liquidates their portfolio to pay for living expenses? Also, if I use the Social Security Administration mortality tables the joint survival probability is still around 75% for a 110 year old male and 106 year old female (https://www.ssa.gov/oact/STATS/table4c6.html), so the core capital needed is very high. Is there a better mortality table to use or am I calculating joint survival probability incorrectly? Thank you for your thoughts on these questions!