Selling the property is not an automatic breach of your lease agreement. You should read your lease carefully to see if any of your landlord's actions rise to the level of a breach. Most likely you are obligated to pay through the end of your 6 month term, unless your lease specifically identifies the sale (or attempted sale) of the property as violation of the lease.
It sounds like something has gone wrong with your case. Landlord & Tenant actions are typically given expedited path through the judicial system. If your case has been sitting for over a year and nothing has happened, I'm guessing that something has fallen though the cracks.
It might be wise to buy 30 minutes of a local attorney's time to try and sort this out.
These are all very good and important questions. However, there is a bit too much to handle in this forum. If your mother's Estate is solvent (i.e. there are more assets than debts) it is important that matters be handled quickly and efficiently. It is very important that you sit down with an attorney soon and plan a strategy for how you should proceed. Unfortunately I have seen many cases such as yours where the property simply starts to disappear. If you have access to the house, it...
I can't believe that the police won't show up. If you and the neighbors are unable to get the police to deal with this, your only other option is to file an Eviction action before your local District Magistrate. Upon receiving an order for possession, you can take that to the Sheriff's office and get these squatters removed. Unfortunately, under PA law you are not permitted to just change the locks on someone who claims that they have a right to possession.
Read your lease very carefully. If the lease does not give you clear guidance on how to proceed, you should contact a local Landlord Tenant Lawyer to help guide you through the eviction process. Under NO circumstances should you exercise "Self Help" (ex. changing the locks, disconnecting utilities, etc.).