thank you for your query.
Firstly your ultrasound
scans DO match your LMP.
is calculated from the date of the last menstrual period, and not from the date of conception / ovulation.
As per your LMP, on 13th February , you would be 7 weeks and 3 days, while the ultrasound had a difference of 4 days ( which is within normal limits of error of the ultrasound machine ).
Regarding 25th February, you should have been 9 weeks and 1 day by LMP, and you were 9 weeks, so that too matches perfectly.
It appears that most likely you conceived from the acts of intercourse with the first person, and not from the second guy ( 16th january )
However, please remember that the only 100 % confirmatory method would be to undergo a DNA paternity testing.