vomiting: reflux, rotavirus, or NGT feed problems

I have a 6 mo old peds pt with hx of reflux and recent rotavirus. He got the rotavirus while in the hospital to get his NGT for dx of failure to thrive for months prior. He is still vomiting at home per mom. The twin sister of baby got rotavirus too. 2 days out of hospital I do my open case visit. I found out she is giving both babies multivit liquid with same vial and dropper. She has told me she cleans the dropper with boiling water for only a few seconds before using with other child and before putting back in vial. Is this sufficient enough or should she have 2 seperate bottles and boil syringes longer and for how long? Also is it possible she reinfected the pt with rotavirus from the twin by doing this? how long to boil nipples and bottles? In this case of both babies with rotavirus, can they be giving it back and forth to each other or will it eventually reslove on its own? Sorry, not sure if the pts vomiting is from rotavirus or reflux or NGT feeds too much.