My mother got her retirement visa on the 1st of Aug this year while my father came over on a Non-Imm Multi O on the 7th Oct, were looking to get my father onto a retirement also but with finances tied up in term deposits etc and varying date requirements for 800k seasoning its proving a problem thinking of the best way to go about it.

Is it possible to add my father as a dependant onto my mothers retirement visa? Or is it done at the time of my mothers application?

Failing that, if I have 800k seasoned for my fathers retirement visa, 2 months later my mother will need to start seasoning her 800k, is it possible to just top up the previous 800k that I used for my father?

Only one has to have retirement extension if in a legal marriage. Now that extension is in wife passport he can obtain an extension of stay. He already has the required non immigrant visa entry.

If your mother has an extension of stay based on retirement then your father can get a dependent extension of stay that is piggy backed to your mother's extension. He would need a non-immigrant 'O' visa to get started, but no money need be shown at immigration.

OP says mother has retirement visa. The two following replies refer to extensions. Can a spouse piggyback on an O-A visa, or only on an extension?

OP says mother has retirement visa. The two following replies refer to extensions. Can a spouse piggyback on an O-A visa, or only on an extension?

Extension only. Where does the OP mention an 'O-A' visa?

Suspect the Op has just used wrong terminology and means extension of stay, because you do not have to season 800k if applying for Non O-A (retirement) visa but do for extension of stay based on retirement. For dependency extension of stay, the primary party has to be on extension of stay.