Bounce it off the ceiling. Even if it is dark wood and soaks up some light you will be much better off than with direct flash.
Go ahead and plan on pushing at least a stop as well to maximise the strobe. I would stage the group evenly across the room shoot one half for.six frames then the other half allowing for some overlap. Print the best pic of each half then mount them together on one board like a Hockney. If you have the baby's family in the middle and they are in both frames so much the better. They will love it.
So just Max out the flash bounce it and take a meter reading. You'll be good to go.