Sister said nasty thing that my fiance has fathered two kids?

I'm about to get married. I'm 41 and with my partner 16 yrs. He just had committment issues but i have him an ultimatum. I'm having my dream big white wedding in 2 weeks time. My sisters after upsetting me here really bad. My fiance had a few meaningless flings throughout the 16yrs i've known him. Basically cheap tramps ofering themselves to him on a plate. I dont blame him, i blame them and i dont speak to two of them, they were 'friends' of mine. Who needs enemies eh. thats all behind us now. I've told my family make an effort or i'll cut ties with them. They dont like him coz they think hes a jerk coz hes not all 'family man' like their boring jerk off husbands. anyhow, theres a nasty rumour doing teh rounds that my fiance is the father of two kids in the neigbourhood. My sisters after telling me. Is she just being nasty? His last fling was 2 years ago and these kids are 3 and 5yrs ..same woman. This is not possible?