I finally got the baby gate up for the stairs. It is probably just in time as she is starting to walk and was using the stairs to get to standing.
Because it was a difficult area I had to find the perfect baby gate, but I finally found it! KidCo Configure Gate is specifically made for awkward areas and they even showed stairs like our in the photo online. We didn't need all the parts that came with it as it was a smaller opening. LT will probably be upset as now he cannot sun bathe on the stairs as he is also locked out with Callie. However the upside is that because of how its installed there is a small spot under the stairs between the gate where Manny can still sneak through. LT and Callie wont fit through the space but Manny does. So lucky for Manny he will have a safe space to get away from LT.
It has been up for almost a week now. I did have to reinstall the brackets on the wall as the screws were just pulling out of the drywall. I knew that would happen but I installed it with my sidekick Callie and tried to do it as fast as possible. It is now more secure with the mollybolts to hold it on the wall.
Manny has been able to go up and down as he pleases and so far no issues with LT and Manny and we have not been separating them.