This one has only one solution! 'Assisted removal'! And Baba dogo is a 'high resistance' area. They will mobilize even the neighbouring plots. So your friend will need a large number of well organized movers. The sooner he does it, the better. The longer they stay rent free, the more their sense of entitlement grows.
Simple policy. Someone f@cks with your property, f@ck him up!!! No discussions! Where the hell was he when you were building?? Don't let a bunch of idiots mess with you. Newton's law of motion: For each action, there is an equal and opposite reaction! Only don't make the reaction equal. Raise it a notch or two - to compensate for the inconvenience.
Talk to @mawaider.
Never count on making a good sale. Have the purchase price be so attractive that even a mediocre sale gives good returns.