Odd night sleeping pattern

Vcurrado

I have 8 week old b/g twins, and right now as most parents do, we are keeping our LOs on the same feed schedule at night, feeding and putting down at the same time. Once they're down for the night they sleep for a good 4.5-5.5 hour stretch and back to sleep easily, but after that wake, they're stretches are short and unpredictable. The rest of the night they're up every 1-2.5 hours. They are drinking plenty after that first wake. Anyone been through this or have suggestions to get the second half of the night more regular?
We have 2 other kids and they were always consistent with their wake intervals.. Every 3-4 hours..

-tired mommy