i dont have anything different than what Suzy have said about 1,2,3.
regarding 4, you have to find the relationship between the main beneficiery, and his/her dependents, this providing that one or more are dependent on the main one.
if there is no dependency relationship between the different beneficieries, then each one should have his own suit.
in case this dependency relationship exist, it would be premature to to try to establish a dependent the right for a benefit, before the main benefciery have aquired his own, because that is the principal element on which the depedant/s would even be entitled to such benfit,
in short
the main beneficiery have to aquire the benefit being sough-green card, ornaturalization- before the depedent can be techenically ask for the right of their derivative benefits.
a family memebers filing for teh same benefit, in a completely separate application, each one have to file on his own.
but on another, like we have recently, a bunch of peoples can file a law suit, against uscis, they dont even have to be related, but each plaitiff have to state separatly his/her own condition, and factual aspect of his/her own complaint, exemple is one case that was posted here not too long ago, in which a group of people suing the uscis over the delay, all in one complaint, how ever noe of these people is related to the other, and my guess that the court, will handel eacg case as a different , concidering the unique circumstance, and there for granting one or moe of this cases, doesnt autamically mean that the other is granted.