What does the underlined part mean?
On 1997, Sean married Cruttenden, (his on-set wife), Jane Sharpe.
You have not underlined any part.
If you mean on-set, I presume it means the woman that appeared with him in an acting role as his wife.
Another term that is used is 'screen wife/husband'
It is not clear whether Cruttenden or Jane Sharpe is the persona of his on-screen (on-set) wife.