Should I resend the emails if professor do not reply to my email?
Do not send too many emails-- this will undoubtedly annoy a professor who is possibly on vacation somewhere when they return to see 10+ emails from the same undergraduate(?).

As to your second point, that is absolutely a no. Why are you even asking professors with whom you are not close enough that they do not even think that your major is related? 

I feel like you may have more major problems, but I would not send more than a couple of emails at this time. If anything, the fall semester will begin soon and you can approach any professors in person to ask for a letter.