Tourist(B2) visa - DS160 submission

[kspsan]

I am planning to bring my parents to US on tourist visa. Below are some of the questions I have

1) Do I need to submit separate DS160 forms for my mom and dad?
2) Can I schedule their visa interview together for the same date and time? If so, how can I do that?
3) Can I submit DS160 form now and then book the visa appointment as and when dates are available?