It took my husband about 10 years to accept that our son had a real mental illness - it wasn't faking for attention, it wasn't that he needed a girlfriend, it wasn't that he was lazy, it wasn't that some secret abuse had happened when he was a child. I hope your husband gets there.
My son's new-ish thing is that he's Jesus too. These past few days, he keeps asking me why he hasn't been crucified yet.
I just keep telling him it's a nice idea to be like Jesus, but he can't be Jesus, and that I know because I'm his mother. And, that he hasn't been crucified because he's not supposed to be, and it's not going to happen. Sometimes it helps, sometimes it doesn't. Yesterday, he asked me if he was human or not - that he was afraid he wasn't. Once, it was phrased as "Am I an abomination?" Later, it was more of a statement - "I'm afraid I'm not a person"
Our family is not religious at all by the way - He's picking this up on his own, but I'm being told that's common.
Upping his meds should help. Seroquel wasn't effective for my son at all other than he said it gave him a mellow little high. Zyprexa in the past would snap him out of anything within about 48 hours at first - then again if he had stopped taking his meds. It stopped working for him very well about a year or a little more ago, and now nothing is working perfectly - still trying to get a good mix going.