Reduced milk intake 14 weeks old twin

[Raisha01]

Hi
I have 14 weeks old twin boys.. i noticed the older one suddenly reduced his intake of milk formula from 5oz to 3oz every 3-4 hours.
Im getting very wortid because thats a significant drop. I was windering if anyone went through this and is that normal.. im getting quite worried as i thought the older they get the more they drink.. please help