Hi,
In theory, you can use this experience as long as you have a reference letter in the required format:
"The following documents are
mandatory for each work experience declared:
a reference or experience letter from the employer, which
- should be an official document printed on company letterhead (must include the applicant’s name, the company’s contact information [address, telephone number and email address], and the name, title and signature of the immediate supervisor or personnel officer at the company),
- should indicate all positions held while employed at the company and must include the following details: job title, duties and responsibilities, job status (if current job), dates worked for the company, number of work hours per week and annual salary plus benefits;
http://www.cic.gc.ca/english/resources/tools/perm/express/intake-complete.asp
However, as family businesses are often abused, you will need to provide as much as you can to prove that this is genuine experience. So income tax returns would help, also add contracts of employment and, if possible, business registration documents to prove it is a genuine business.
All the best