Hi, Sorry I can't be of help - but a few thoughts
Do you know WHEN / WHERE - Fred ASSELIN - married Mary n/k
Do you know When/ Where the children Ronald, Philip and Margaret ASSELIN were born ?
You know that Fred ASSELIN - passed away in 1980.
REGISTRATION of DEATH - Long Form Death Certificate
Depending on requirements of the time - and knowledge of the Informant [ could be Mary]
Will show personal information - Including name of spouse - Maiden name.
Have you searched for an OBITUARY - this may show names and locations of other family members at the time
REGISTRATION of BIRTH - for Children - will show Maiden name of the Mother
REGISTRATION of MARRIAGE -for Children - will show Names of Both sets of parents - Including maiden names of the Mothers.