Your last period started on 14 November.
Sperm can survive up to about 5 days. You likely won't ovulate until sometime between days 11 and 16 of your cycle. The egg is viable for about 48 hours.
You had sex on 16 November, day 2 of your cycle. It is extememly unlikely that you'd get pregnant. It's too early.
Having sex on 24 November, day 10 of your cycle, there is a strong chance of pregnancy.
Having sex with #2 man on 26, 27, and 30 November, days 12, 13, and 16 of your cycle You'd be near peak fertility. There is a strong chance of pregnancy.
Sex with your boyfriend on 4 December, day 20 of your cycle is likely well past when the egg would be viable. It is unlikely you got pregnant then.
Your due date is based on your LMP. It matches. Take your due date and add 40 weeks and you'll get 21 August. It is NOT exact. Doctors base due dates on your LMP because most women know exactly when that was.
There is no way to know exactly when you conceived nor when you ovulated after the fact. It does take several days for fertilization and implantation to occur.
You'll need a DNA test.
You can't say "who's sperm enters" the fallopian tubes first. It's not just that there is sperm, but was it viable? While it can last up to about 5 days, most dies within hours.
We can't tell when you ovulate after the fact either, no one, not even your doctor can.
A DNA test can confirm paternity. Good luck.