Can I sponsor my parents and Inlaws the same year plz help?

[zombie]

Hello everyone,
I am a housewife living in NJ for past 2yrs. My husband and I want to get both our parents here this year to visit us during summer. We have planned my parents and Inlaws visit a month apart. Both my parents and In-laws have decided to pay for their own trip and We are going to sponsor for their stay here. They plan to stay about 6wks each. My questions are
1. Is it ok if we plan to get both our parents here the same year?
2. How many months apart do they need to apply for the visa?
Thanx

[immihelp]

1. Yes
2. There is no such rule.