help in applying for parentsand sister

[monax]

First of all I want to thank this web site who help me to solve my confusion.Ihave few more question if some body help meI realy appericate that.
1. My parents dont have the marriage certificate what other doc they can use.
2.I have sister under 21 do I need to file a seprate petion for her. or she can come with same petion.OR what kind of form i need to file her as a dependent. :

[immihelp]

1. https://www.immihelp.com/marriage-ce...a-immigration/
2. Don't need to file separate petition for her. Just write her in name one of the parents' I-130 petition.
https://www.immihelp.com/family-base...on-procedures/