The probability is way highest for pregnancy from sex Feb 16th. Do you remember your sex drive was particularly high, an indication of ovulation? Feb 9th was too early in the month to have much of a chance of success. You must be 37 weeks by now. Best of luck.
By all means, do a DNA test when the baby is born. Guy A had a lot of chances, especially since the sex was unprotected, but the app and the second ultrasound keep Guy B in the picture (if the protection did not in fact protect). The best way to know for sure is to do a DNA test when the baby is born, with both men.