"The" false "doctrine of the perpetual virginity was held by both Luther and Calvin. Why is your reading of Scripture to be preferred over theirs?'"
The Catholic church has castigated Luther for centries; now you want to use him as a source? Calvin also taught predestination which the Catholic church rejects. How do you separate their true beliefs from their beliefs which you consider false.
Your best bet would be to ignore the teachings of all men. including myself, and learn to study the Bible for yourself. It is really not that difficult.
Robby's point still remains. You study for yourself and conclude that two sisters Mary named their children James and Joseph. Most everybody else concludes different. Surely Luther and Calvin did not decide on the perpetual virginity of Mary because the Catholic Church taught this. So here we have you, Luther and Calvin, all believers in Sola Scriptura, concluding different things based on the scripture alone. You don't find your methods cheesy?
The point being that your interpretation of the Bible has no special authority.