@Sao311tigger The configuration in your pic should work. I've done it with a residential rental row house with each apartment having a small, fenced back yard. So, if it is not working for you, I suggest you try with a fence that a sim can't step over. I also see a short fence on what looks like a 2-tile wide porch. You need to break that and put in a stair (sorry, just being Capt. Obvious) so there is an entrance into the back yard that the game sees. The back yard, since it is outside, should not be assigned to a specific apartment to keep the rent lower if you don't have the entrance from the apartment. Fences will suffice to keep other apartment tenants from entering the back yard unless you add fence gates.
One thing about residential rentals when doing what you are trying to do. When an apartment has 2 doors, a front and back door, the game tends to get confused which is the front door and will lose the setting on travel especially if you use a foyer and have the apartment front doors open into the foyer.
Hope this helps.