There's really nothing to be done with. dad isn't serious. He isn't actually concerned about convincing anyone about his far-fetched fantasies. I have doubts whether he even really believes what he writes, because he has many of the marks of a dedicated Poe, but because of that law it's nearly impossible to tell if he is really a deluded fundamentalist or just faking the part.
Regardless. Even assuming he's being genuine. dad spends a great deal of time posting on this site and "defending" his ideas with a "rubber and glue" approach. He likes posting on these forums because within the little fishbowl of CF, he can pretend to be a great debater, defeating one non-believer after another in his own head. And he can do so because there are enough like-minded fish in the CF bowl that will agree with him... or at least take his side in a "bible vs science" breakdown.
But this is not something he can do in real life... and I'm fairly sure he knows it. Everything he posts on these forums is so B.S.C. that if he plied this to a live audience of non-believers, the laughter would be just too demoralizing to bear. dad would be the worst kind of evangelist in real life if he actually said these things.
So ultimately, trying to debate dad is useless, in the sense that you won't get him to admit to anything. He doesn't have to, he doesn't have an audience holding him up to real scrutiny. It's far better to just treat him as the clown he acts, and let him decide whether he wants to put up with that or not.