Question /opinions

At 66 yrs old i find myself in a position that i regret... how do i tell my son and daughter that their father is not their father but actually their grandfather... booth were conceived when their father was at work and i had asked their grandfather to help fix a basement door that's when my son was conceived .. my daughter was conceived 2 years later just because i called him for a sexual encounter..... in between both births we had several sexual encounters and i don't know why i allowed it to happen ... now they're on their own and have their own families .... should i just write a letter to explain when i get laid to rest ?