This is one of the reasons why people stick with rules within organizations, rules with which they may not necessarily agree.
My Dad had a 40-year career with the Seventh Day Adventist Church. He is retired now and getting a pension from the Church.
Imagine if I tried to convince him their approach to Sabbath observance is rooted in the Old Testament, not the New Testament. After 40 years of economic, social, and spiritual ties? I probably would be wasting my time. The mere fact that a switch in beliefs would look or sound hypocritical may be sufficient to prevent him from listening.
And he would have a point. If an organization celebrated you for about 40 years, such that you rise to the top of the organization, any switch in beliefs will have to be internally validated between him and God, not externally visible. The fact that he never would embark on external validation of my truth would prevent him from agreeing with me in any argument on the subject.
So what do I do personally? Whenever the family is together, I never bring up theological differences. I love my parents, support them financially. In the same vein, they never attempt to convince me they are right. Our relationship simply emphasizes commonalities, does not revolve around our differences.
I deliberately set this tone because it is exactly the tone I believe Jesus expects. Jesus always emphasized practical love. The woman at the well? Jesus did not preach ‘thou shall not commit adultery’. Rather, He preached, ‘What you have been searching for via serial adultery that leads to marriage, you can find in me’. See the difference in tone? The focus was not on theological demands. The focus was on that woman’s search for fulfillment, satisfaction in life.
Jesus was never judgmental. He always was about taking us from where we are — all of our wrong notions of satisfaction — to where we ought to be. The focus was not on some demand, but on us, our satisfaction, our fulfillment.
Whenever there are theological differences within family, it is best to focus on loving each other, and not attempting to convince each other. When the love walk is genuine, even when family do not explicitly change, they are influenced to one degree or the other by genuine love, such that while they remain tied to some religious organization, internally they can begin to validate the truth for which we stand in their personal walk with God.