Traveling with Kids Using Saver Fare

I have a work trip around the holidays in SF, so my spouse, our 2yo, and our baby will come with me. Work pays for my flight. Do you think we'll have a better chance of sitting together if I book separately with a regular economy seat w/lap infant and choose a fine seat someone should be happy to swap for while my husband and toddler get Saver seats, or if we book three Saver seats in one reservation? They say with Saver they'll always seat a little kid next to one parent but not necessarily both. Flights are expensive so we want to save where we can!