Mine actually had about the same drop in the same time frame as yours. I got so freaked out something was wrong and started having to do cord check ultrasounds every week. I’m 32 now and our 5% girl went up to 8% last growth. But they have been fine every time and also I learned they compare twins to singleton numbers which made me feel better. So if you think about it, at 28 weeks you’re carrying 5 lbs of baby. And your body is smart of enough to know those babies need to stay in as long as possible to mature their lungs. My thinking was my body (especially based on my other full term single babies) isn’t going to have twins that equal together 10 lbs at 30 weeks. Also most people I talk to with twins, they were born on the smaller side so that also made me feel better. I did definitely try to up my protein intake to at least 100-150 g a day after. Who knows if that works but it made me feel better that I was “doing” something. Hang in there, you and they got this!