Hellobee Boards

Clockwise: DH (and highchair), MIL, Brother, Brother's GF, you, Mom, SIL, Dad?

This may be a bit heavy with the guys towards one end, but I think it still pairs MIL/SIL together and Bro/GF together.

My suggestion would be to put MOM and DAD on the same side but on both ends, so they won't be able to look at each other easily. And then I would put the person that will talk the least in between those two so the majority of the talking will be across the table. Something like this
. YOU
MOM Bro's GF
SIL Bro
DAD MIL
baby/Husband

@TemperanceBrennan: I actually agree with this, having MOM and DAD be seated on the same side so they don't have to look at each other. Even in friendly social situations, I don't always interact with the person I'm next to or two seats beside me.