How to create a contract between 3 people about selling app in Google Market

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What is the name of your state (only U.S. law)?

 

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OK for some reason the text I typed earlier did not show up.

I have two friends who live outside of United States and they write applications for Google Play(Google Market) .They can not sell apps because Google Play is not supported in their country so they want me to sell the apps for them(I live in California) but since we're dealing with money we decided to have some kind of contract/agreement.
The agreement basically needs to confirm that I will publish the apps under a specific Google Play account named XXXXX and that my friends will get some XX% money from the sales revenue.We will sign the agreement electronically.

My question is, do I need an official apostille for the agreement or can it be done just by individual signatures? What type of agreement should we create(legal name, like NDA e.t.c).Any example would be greatly appreciated.

Thank You !