My Dad is refusing to get a second opinion - what can I say?

My Dad (68M) has Stage 4b (Gleason 9). He’s been on ADT for 7 months and his testosterone is down to 0.03, which we’re happy about. But his doctor won’t let him do repeat scans to see if the tumors are shrinking - despite us continually asking (he keeps saying they won’t show much). When asked (several times) about if he should be doing chemo or radiation, all he says is “it’s not time yet.” When asked if we can test to see if it has any mutations (like BRACA, TP53, etc), he again said that “we’re not there yet.” He basically just keeps saying we’ll only do ADT until he becomes testosterone resistant and then we’ll try something new. My sibling and I have been begging him to get a second opinion since day one, and now that his pain is getting worse, we’ve been pushing for a second opinion even harder. But he won’t do it. He said his doctor is Ivy League trained and therefore he’s a good doctor. But I just can’t accept this is his only options right now.

Please let me know what I can say to help convince him to get a second opinion. Or if I’m in the wrong, please tell me.