Tenant wants shared yard split

[Houston Groff]

I have a 2 unit in Pennsylvania. I'm dealing with a newer tenant who is supposedly disabled( some heart condition) who doesn't get along with the tenants in the other unit( they have been here for years). I've had complaints about noise, parking, harassment from these tenants since they moved in about the tenants who have been there for years. They have even sent no contact letters to the long term tenants saying the interactions are not good for the gentleman's disability. Now they want the back yard split to help enforce their no contact letter. There is nothing in the lease about the back yard being shared or split. When they moved in they asked about the yard and we told them it was shared because it had been before and was never an issue. Now it apparently is a big issue. We don't really feel its right to take it away from the long term tenants who have children. Plus there is one walking path from the parking lot to the units. We don't feel like we really have to accommodate with a fence or some kind of divider. We are thinking of telling them we wont be doing anything about the yard and maybe even giving exclusive rights to the other long term tenants and giving them the option to break the lease early and leave if they wont agree. Appreciate any help or feedback.