My 2 year old twins have strep throat and have been taking anitbiotics since monday. One has a barky sounding cough. Is this still strep?

No, most are viruses. The fact that strep is found does not mean that strep was positive of symptoms. Most cold-type illnesses such as that with your twins' cough are viral. Probably initial symptoms were viral-related. Swab was done in strep was found. There is a latin expression "post hoc ergo propter hoc": meaning: since strep was found, it is presumed to be the cause of symptoms. Not necessarily so.
Cough and strep. This needs to be reported and discussed with the treating physician as it may be a complication of the strep or a new condition. Re-evaluation is in order if the condition is getting worse or changing.