While I like the thoughts of Slimboyfat on page 12, your family won't let you fade away without pressuring you toward baptism. They think they are literally saving you.
You have already chosen a path of resistancecthat includes doubting the doctrines. Great. I like how Defender of Truth says it on page 13:
"Generally speaking, be polite and respectful, and let HIM try to convince YOU. He won't be able to. He may even find that his reasoning comes up short.."
You can brush up with people here and at jwfact.com. But don't be an expert like you have been reading outside materials. Simply end with how you just aren't sure enough to fully accept the things said.
1914- the math of using 360-day years to apply a rule from various scriptures about a-day-for-a-year. Then they had to change the definition of "generation" to keep that date. That's as deep as you need to go to say, "I'm just not ready." Throw in, "How did you feel when they changed the meaning of generation?" If he gives you a standard statement of blind trust, just say how you are not there yet.
You have done so well. Remember your ultimate goal is to keep these family members in your life and you will do fine.