2nd child car seat

Where do you plan on putting the second child car seat? My son is 2.5 now he sits forward facing in the center of my Ford F150. I assume the newborn should now go in the middle bit where does the 2.5 year old go? I thought it was safest to ride on the passenger side because most times the passenger airbag is off when I drive alone. My husband thinks that we should leave the 2 year old behind the driver because idk about all F150s but mine is 2015 and a portion of the backseat on the passenger side lifts up if you want to put something big in the back seat. I think it's a dumb reason. Also my cousin has the same truck with an infant and a toddler but I didn't question her yet (because if I don't agree she'll wonder why I did opposite lol) but she had had the car seats on the sides and nothing in the middle. Just asking peoples experience or trying to get a good idea of what's best.