Photinias not growing

The larger Photinia on the left near the front of the car and the smaller ones on the right were all planted together, 2.5 years ago. I got them from Bunnings at the same sizes and planted them together myself.

This front yard is at a slope and my dad said this the front ones don’t have enough soil depth. I’m not an expert at this.

Does anyone know why the front ones haven’t grown at all while the back one has? If it’s due to the soil depth or quality, can I fix it myself?

This is in western Sydney.

Thanks in advance