I Have Twin Girls That Are 7 Weeks Old Today

I have twin girls that are 7 weeks old today they were born at 33 1/2 weeks and we have been breastfeeding but topping off with formula (to make the required weight) Julia (the slightly larger twin) hasn't passed a stool in over 72 hours and Ava hasn't in about 48 hours we have tried the massage with a clockwise motion and the bicycling the legs but still nothing, just wondering if there is anything else we can try and if maybe if this is normal.