I agree with Meysha. The first one is fine as you have indicated. The subjects are lit appropriately with nice soft light that shapes the faces. In #2, the lighting looks flat, so you obviously used a flash to overpower the backlight which was quite strong. Choosing a less bright background would have helped in this case. In #3, a reflector positioned quite close to their faces would have provided some nice fill light, or using a fill flash with some diffusion. Same thing with the last one.