Answer: It is a bit difficult to answer this question without knowing how long the answer should be - 200 words? 300 words? More? Anyway, in outline, I would address the social influences in the order that they appear in the question.
The whole play is about social norms - how the values of others (our peers) influence our decisions, influence our lives. By far the most significant of the three "topics" in the question is the family. The Montagues and Capulets are at war with each other, in effect. Although the play is set in Italy, Shakespeare's audience would have picked up the English context, and, ironically, the themes of the play became more real during the the English Civil War which began a relatively short time after Shakespeare died. This divided families in England as the Capulets and Montagues were divided in Italy. The love between Romeo and Juliet was thus "forbidden" from the outset - this is the basis of the tragedy that the play is: they are doomed to suffer, although not necessarily die, because of a feud between their families, which is, ironically, resolved by their deaths.
There can be no happy ending: this fatalism is characteristic of Shakespeare's plays. He is alluding here to elements of Greek theatre that influenced him, where character's lives are shaped by Fate, by forces beyond their control. Although to the audience, Romeo and Juliet's love appears real, the audience knows from the outset that because of the family feud, the relationship is not going to end well. From the outset, the love of the two characters is going to be destroyed by the feud between their families - the most important social influence on the two.
All of Shakespeare's plays have a "moral theme" - they were written to give the audience a lesson. There are many lessons for humanity to be drawn from this play, some of them not so obvious, but the most obvious one is the danger that arises for society as a whole - not just for two young people - of hatred, of silly disputes between families, especially politically powerful ones. The play is thus a critique of the forces at work in England at the time Shakespeare was writing that led to the English Civil War. Although reference to religion is not explicit in the play, for the audience, they would have been aware of this theme. Romeo and Juliet's love was not illegal - even given that, from today's perspective, they were to young to consummate their relationship; they are destroyed not by the legal system but by a more basic social relation, hatred, conflict, and conflict based on what? We never learn what the basis of the familial feud is.
What religion are Romeo and Juliet? We are never told and that is, in itself significant and not significant, insofar as their religion is on one hand, irrelevant. One could have been Protestant, the other Catholic, but Shakespeare necessarily shies away from making explicit their religious allegiances although the play is a call for religious toleration, an attack on the religious schisms of Elizabethan England before the Civil War, and the play is a plea for toleration and understanding, not just in a religious sense, but in a secular sense too.
Little reference is made to the laws of the land, although Romeo's banishment gives us some insight into the legal codes of the time. What is far more important is the family ties and the dangers inherent in these, for it is these that bring about the tragedy as much as Fate - missed communication for example. Shakespeare was trying to warn us of the dangers of silly disputes becoming blown up to such an extent that they lead to deaths.
Step-by-step explanation: