It never hurts to do a DNA test, even when things seem to be adding up as you expect.
I would suggest the dad is the second guy. The first guy is just a couple of days too early, even giving the average length of time sperm is said to be able to live in a woman's reproductive tract.
Hi, what is your due date? Was it given to you at the time of the ultrasound that said you were 8 weeks 5 days? (Was that given to you from an ultrasound?)