baby reject formula milk

hi, i am a mother of twins. i breastfeed them and express my milk if im working. lately my my milk production tremendously drop even ive expressed my milk every 2 hours at office. i start consume milk booster but seems like my milk do not enough for them both. i introduce formula milk for the babies, twin 1 can accpt. but the twin 2 reject all formula milk. he vomit every time fed by FM, his stool become green. i already gave the Twin 2 tried many brands but still rejecting all. S26, frisolac, frisolac comfort, lactogen, dutch baby, anmum and snow. all rejected by the twin 2. anybody experience the same issue? what ur opt or solution with this issue. let share with me.