What messages are being conveyed by Shakespeare about arranged marriages and parent/ child relationships is the seventeenth century?
In my opinion, it is sort of dangerous for us to try to say what message Shakespeare is conveying to the 17th century audience. Our own mindset is so far removed from theirs that it is hard to know how they would have perceived these characters.
To an audience today, it seems that Shakespeare is saying that arranged marriages are bad and that relationships in which the parents are able to dominate their children -- to force their children into things like arranged marriages -- are bad too. It seems that Juliet (at the very least) would be much better off if her parents had not tried to force her to marry who they wanted her to marry. If her parents had acted throughout the whole play the way that they do in Act I, she would not have died.
So that's what I "hear" when I read this play today. And that's how I'd answer the question. But I am not certain that that is what a 17th century English person would have heard.