So in the question #3 about number of people in this application - leave it as it is - 1 (just mom)if you just mention him in the form, your family size won't change. There is a field saying something like "dependent accompanying principle applicant to canada", you have to say no there and give reason as "He is already canadian citizen and other reasons why he can't sponsor..." If your dad is working then you can include his income as well!!
and in question 13 about dependents - add my dad?