Parent invitation/visa?

I am pregnant for 5 months now, due in early Oct. Plan to invite mother or sister to come for my delivery. Does anyone know how long it may take now to get a visa from US Beijing embassy? and what are the documents they should bring with them?

Also,since my mom will not be able to stay on, she wants to bring a nanny along. Is it possible to invite a nanny from China? _:o

I am totally ignorant, appreciate any replies and kind help!