No, you cannot do that in Gmail. A Gmail account belongs to one person. It cannot be assigned to multiple people.
No, they cannot be a part of it. People who are not a part of Gmail cannot be a part of Google groups. It is the copyright of Gmail to be a part of it.
You cannot access Facebook account using Gmail. You have to use it using the Facebook site only. Gmail is just for confirming the account.
Unfortunately you cannot change your theme on Gmail on ipad.
No, you cannot send a physical check through Gmail.
You cannot guess any Gmail address. The addresses of gmail belong to the owner. They are like the lock on the account.
You cannot create a Facebook ID on Gmail. Facebook ID can be created on Facebook via Gmail. The confirmation mail is also received on Gmail.
No you cannot do like that ever. You need to have a Gmail account in order to sign in into that. Yahoo accounts signs you into yahoo mail.
You have to delete all others manually. They cannot be deleted automatically by Gmail. Then you need to create the new Gmail address.
You cannot get Gmail account before 13 years old. It is the age before which a person cannot create Gmail. The reason why Google decided this was the children before 13 are not smart enough.
You cannot get the gmail address of anyone by their name. The gmail addresses are unique for everyone. The serve the purpose of logging into the account.
You cannot make audio call on Gmail. However video calls are possible in Hangouts. It is the latest IM of Gmail service.