It sounds like your father was taking one antiviral at a time, developed
resistance, then moved to the next, then
resistance, then to the next, etc. This the the horrible model to what's called "cross-resistance". See this thread for more info:
http://www.medhelp.org/posts/Hepatitis-B/Antiviral-cross-restance-chart/show/519565
Treating a multi-resistance HBV patient will be challenging.