im interested to know as well, and in my understanding :
you are the main sponsor :
for you : 3 ( you, ur husband, the baby)
for the joint sponsor : 3 ( the sponsor, his daughter, ur husband) unless the JS has spouse, then it's 4 like what @Timona said
it's gonna be 2 forms to fill. one for u, one for him. and if the joint sponsor has spouse, another form i-864A