I am building a 1250 sf 2 level home and need advice on my mini split placement. I already have 2 18k mini splits. Downstairs is open area. Upstairs I am planning on putting the 18k unit at the top of the stairs between 2 bedrooms. My concern is running the mini split in a small hall and if the doors are open will it preform okay. Any input would be appreciated.

One really can't give an absolute definitive answer without a room-by-room heat gain/loss analysis and knowing how the rooms are ventilated. For example, if you are using HRV (Heat Recovery Ventilation) system that brings fresh air into the bedrooms thereby causing them to be slightly higher in pressure than the hallway, this may inhibit the mini split from getting adequate cool or warm air into these bedrooms. One should really accomplish an integrated HVAC design that considers all this.

I wouldn't chance it. Majority of the cool air will go down the stairs. IMHO

Just get a second head and have one in each room....then the doors can stay closed and cozy.