co-signer question. parent sponsorship please help

[kelseyA]

I have the low income requirement to sponsor my parents, but don't know what will happen in the next few years with my income. Right now i have enough income for 9 people ( my parents and their two dependents and my husband and 3 kids). Should i file alone since i have enough income? If down the road i do not have enough income, can my husband be added afterward as a co-signer or i have to include him in the initial filing not afterward? my husband is currently unemployed, his EI ended in Jan,2010. So my question is, can my husband be added as a co-signer after the application has been submitted may be in the next 2 to three years if i don't have enough income?