You don't need to combine, there is no min requirement for income for this type of visa as long as you have CPP or any provincial pension income that is for lifetime. You can apply as a couple on either income, but it's almost a 100% guarantee that you'll need an official marriage certificate for that, and even then the final approval ( for permanent ) might come for the principal applicant first and for the dependant later. If you don't have any official piece of paper re your common law status you'll have to apply separately.