No, you can just be on standby to help so long as the other borrowers are making monthly payments in full.

You may choose to contribute regularly and if you do, we can keep account of your payments separately. You can build up an ownership stake in the property if you choose to.

If the owners fail to meet their monthly mortgage payments, then you as the income booster will need to make the full payment, even if you are a standby income booster.