Hard to tell as you never mentioned their profile. Chances are good if their purpose to visit Canada is valid, they have strong ties (job, assets, family.. reason to go back) to their home country and they are financially capable to travel (money on the bank).
They have not shown any finances as my father gave a letter that he ll be bearing all costs.
A bit alarming as your sister and brother-in-law are no longer minors. I don't think that stating that your father will bear all cost looks good on their application.They will be assessed on their financial capabilities to travel.
Maybe not for your parents. Hard to say about your brother without information about his age and current status. Not great chances for your sister and her husband.
So as I predicted the issue is with your sister and her husband. You should wait to see f by chance they get approved but if they don’t they should apply on their own and include proof of their own finances and ties.
