I had period on 7/18 , 8/14, 9/9 and 10/4 had sex with one person on the 13 another on the 16 which one is more likely the father

It can be either one or both of them (twins or more). When your child is born then go to court for a paternity test and have them both show up. Don't guess.

One is my husband the other was a one nightstand. Thinking the 13th cause think I had already ovulated by the 16th but all the sites seem to differ on this

Sperm can survive for almost a week and since the dates are so close you won't know until the birth. But you also mention being married. The legal father will be your husband at the time of the birth regardless of who's DNA helped make the child.

And unless you are taking your temp and actually tracking your fertile times, just the period date does not give you exact times for that.

Next even at very best, give or take a week is the best, people have been known to get pregnant on their period, the week before, the week after.

So it can be either man, only a DNA test will be able to tell.