The maximum spousal benefit is 1/2 of the worker's benefit. So if the wife's PIA is $800 the most the husband can get is $400, but that is reduced by the amount he gets on his own. So the one who files has to make less than 1/2 of the other.

If the person with the higher benefit dies first, it is possible that the survivor's benefit (widow/widower) can be increased to equal what the deceased was getting. But not both.

50% in life; 100% in death. Assuming the spouse/widow is over full retirement age.