The fact that Jesus had a nuclear family is evidence that Mary did not remain a virgin. The Biblical writers wrote in plain language and I give them credit for knowing what terms like "brothers" and "sisters" mean in familial context. I don't have to engage in a lot theological gymnastics in order to re-interpret the Bible in order to accommodate a false teaching that is nowhere in the Bible.
Yes, but those only happened in special circumstances. It was not done in ordinary parlance, otherwise you would not be able communicate in a coherent manner. There were special circumstances where a given word might be expanded to refer to nephew as a son. That happens in the OT, but you can't make that the rule. Those instances are exceptions.
Furthermore, the burden of proof is on YOU, to prove that every instance where Jesus brothers and sisters are references that it doesn't mean what it says, that each of those references are talking about cousins or something else.
Yes, you have to rely on the opinions of fallible men. I rely on the evidence from the infallble, inerrant Scriptures, wholly inspired by God. So my appeal is to a much higher authority.
I don't trust in alleged miracles. I trust the Lord. The fact is that your appeals are always made to stuff outside the Bible and you have to appeal to anything and everything except the Bible. I will put my faith in the unmovable, indisputable rock of Scripture. You can trust in fallible men, if you want.