So you essentially showed flags that your father didn't do well in his business, when you provided a letter of financial support along with employment letter, pay stubs, and bank balance for the last three months.. Your notarized invitation letter holds no value. I don't see any suspicious...
Why not have them land in Canada as soon as possible? Afterwards they can choose continue their healthcare in home country or enrolled for Canadian healthcare.
From the looks, both siblings does not have significant family ties outside of Canada. As they are from India, CAD 11k is probably not enough. Your funds are not considered.
I have no similar experience but not unheard of. Some people were denied entry even visa was granted and later cancelled. This probably a better situation than arriving at the border only to find that one's visa was cancelled (or simply denied entry) and had to get a flight to leave the...