thanks gals! You girls are great for asking questions.
This is what I told my husband! He wanted to borrow from the outside and I dont think his manual says you can.
The PPs have given you some great information. Here's an explanation for your husband if he wants more than a yes or no answer-
Using LATCH in the center without a third set of dedicated lower anchors is called borrowing. It's only allowed if it's specifically stated in both your vehicle and carseat owner's manuals (which Britax does allow, but Nissan does not).
There are specific standards for LATCH anchors, including spacing. And while they may look the same from the outside, there are two ways in which they are connected to the vehicle frame. There is a bar connecting the two anchors for the seating position. Some vehicles are like this: o_o o_o (no bar in the center seat) and some look like this: o_o_o_o (where they are all connected). Vehicles that do not allow borrowing either have no bar in the center to support the anchors or have non-standard anchor spacing or both. (note: some vehicles with non-standard anchor spacing still allow center LATCH, but that's where your carseat manual comes in. many carseats do not allow for that).
Seatbelts are no less safe than LATCH. You need to follow the manuals for your vehicle and your carseat.