This is what responce I got from Tweeter Handle IRCC
May 24
@CitImmCanada Under ,Parents and Grand Parents 2019 Programe Can I sponsor only 1 parent ?My mother. (Principal applicant) As my father has Cancer and is bed ridden and won't be able to travel with her .Your assistance in answering this question is appreciated.
IRCCVerified account @CitImmCanada May 24
Replying to
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Hi, Yes you can apply to sponsor only one parent. Note if you only want to sponsor one parent (your mother for example) then your other parent (your father) would count as a dependant of the parent you want to sponsor.