Just the person who is petitioning you. The co-sponsor will just back up the person who is petitioning you.

exactly, but the petitioner must fill an i864 eve though his incomes are not enough, so in that situation, where the petitioner doesn’t qualify for sponsoring, is when you need a sponsor, whether is one of your or your huband’s family members who lives in the same house as you, or someone else who earns enough and does her/his taxes.