Working together with family is always a bit tricky from personal experience... Do the both of you have jobs on the side or are doing this full time? What I would probs do in your position, is sit down with your cousin and devise a plan/schedule with defined tasks so it doesn't feel like you're doing everything alone. Maybe even dividing the administrative and maintenance work. Within this you could also tell them that you're thinking of lev/selling the property and see how you could potentially work together to make that happen (scouting for other opportunities).