In this case he is qualified without a cosigner but he added to ensure in 2019,2020,... he is not have enough income she MAY help him. Because if he did not add her as a cosigner later on he CAN NOT add a cosigner.for co-signer >>co-signer must provide proof of income for the last 3 taxation years before the date of your application
https://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=1461&top=14
both think have to consider before going to CIC
He needs to send supporting documents showing his family size 2016,2017,2018 to cic.