This totally made my day.
However, to actually answer these questions:
1. I'm fairly sure this has been covered before, although it's never been in the official FAQ. A character cannot materialize themselves within an area that is already occupied by matter. Materialization works by imbuing ectoplasm with energy that allows it to permeate the veil and enter the physical realm in an analogous form. Just like you can't pour any more water into a glass that is already full, you can't materialize in an area occupied with solid matter. If a character attempts to materialize while passing through a solid individual, they materialize in the closest unoccupied space.
2. Hahaha. That's all I have to say about that.
3. This too has been covered in the past, during the entire "Can a ghost get someone pregnant while material?" controversy- although it was never documented in the official FAQ. Certainly, a spirit could TRY to donate an organ to a living being. However, whenever something leaves the material form of a spirit, it dissipates- for example, when a character's weapon is disarmed, it merely disappears. In the same fashion, any organ, tissue, or fluid removed from the physical form of a spirit would dissipate immediately- whether it be a kidney, a lung, blood, or even semen.