Q: Can joint sponsor combine his household income? length of employment?

My Brother has offered to be my Joint sponsor for my spouse. He is married with a son and a step daughter. Their household is 4, with my Husband it would be 5. His income is not enough to cover a household of 5 but his wife also works, their combined income would be enough. Since they are one household can he use her income and sponsor my husband? Both of them have only been working for 3 months at their current job, will that be a problem? Before this job they had a break in employment for 6 months.

This question hasn't been answered yet.