Hi,
When you sign the visa application and the Family Information form, you certify that the information contained is complete and truthful. Also, the information you provide will be used to verify your family information for any future applications.
In case the information is incorrect/untruthful then CIC may consider the applicant to be inadmissible.
Even step sisters/brothers or half sisters/brothers must be declared.
It's not possible to say how the visa officer may consider the new information about your siblings (who were not declared in your previous TRV application) in your new TRV application.
You can do the following though:
When you reapply for the new TRV.... you must declare all siblings and their details.
To support your statement, you must provide evidence like birth certificates/ passport copies (if possible) of the "undeclared" siblings that show you have the same parents. You can also provide an affidavit for the same.
Also, you can provide an explanation that purely due to oversight you had made a mistake of not declaring these siblings in your previous TRV application, and it was not intentional in any way.
Regarding your other reasons for refusal:
Do ensure you provide solid ties to your home country (employment/business/family/property ownership/financial situation/any previous travel to other countries, etc.... and provide strong reasons that you will return to your home country
Hope this helps
