Old-D
Sir Fred and Lady Penelope Emeritus.
... I fear you disappoint me again.
As I'm sure you well know, unless of course the lovely Penelope Emeritus was the daughter of an Earl (or more senior peer) she would be Lady Emeritus, or, more formally, Penelope, Lady Emeritus.
Many make the mistake, even the individuals concerned (accidentally of course
). I do know of a retired 4* who wrote to his (about) 3 or 4 time successor in post noting "your staff seem to continue wrongly describing your wife in official correspondence!"
Good drills methinks ......
and wouldn't your Headmaster say "Call me Patrick!"