I'm a student and I applied to many internships over winter and only ended up interviewing with 5 in total, one of which (company A) gave me an offer for a different, less relevant internship after declining me for the one I applied for. Although this internship is only semi-relevent to my degree, the pay is very decent and I had been declined by or never heard back from the other companies. I accepted the job offer, did the background check and drug screen, and I am supposed to start in less than a week. The internship is supposed to be 6 months.
Last week out of the blue one of my top choice companies (that I submitted my resume to and never heard back from) emailed me about a dream/perfect internship opportunity. I agreed to interview and then they offered me the position (and the pay is much higher too). This internship is for 12 weeks and starts in May (two months after my 6-month internship with company A is supposed to start).
Do I renege completely on my offer from company A?
Do I Decline my dream internship because of already Having made a commitment?
Do I explain the situation to company A and ask if I can work there for just the 2 months and possibly after my other internship?
what is/isn't ethical and how would it impact my career? I do not care about ever being hired by company A in the future.