#3. Definitely #3. I mostly model mortgage prepayments and defaults, the housing market, and do econometrics-style forecasts. That's not in any of those books.
For good reason!
I'll have to check out Guide to Mortgage-Backed Securities.
I never look at Fabozzi's book these days, but I still break out the Guide to MBS for its appendix on mortgage amortization formulas. That's a pretty weak recommendation.