Well life is interesting

So my husband and I just found out my 18 yr old stepson and his 16 yr old gf who is a mother of 2 already are pregnant she says she’s 21 weeks due Sept.10 but my son says the dates don’t add up to when they had sex dec 4 and she admitted to cheating at the end of nov, her story seems so off, but I don’t even know what to do my hubby and I have been ttc for almost 3 yrs so this was a blow for us Im just looking for advice oh and her dad shoved her down today pulled a knife on my son he’s the primary custodial parent so she’s in the hospital waiting on cps to show up tomorrow to do a safety plan on her.