First and foremost, thank you for your service.
I would direct you to the Pennsylvania Landlord and Tenant Act of 1951, 68 P.S. §§250.101. You should be able to find it online fairly easily. If you frequently rent out property, you should familiarize yourself with this act.
I do not practice in Pittsburgh, so I strongly suggest you contact a Pittsburgh attorney, as there may be procedures specific to that city that need to be followed. In general though, the first thing you need to do is serve on the tenant a Notice to Quit. Since this eviction arises from the failure to pay rent, the Notice would state that the tenant must vacate the premises in 10 days.
If they do not vacate within the 10 days, you can then proceed to file a Complaint in court. The Act requires that a date be set for a hearing not less than 7 days but not more than 10 days from the filing of the Complaint, so there will be a fairly quick turnaround on this. Here is where you will state your case. If the court finds in your favor, it will enter a judgment against the tenants and order that the tenants vacate the premises and pay any back rent.
If, after 5 days after the judgment, the tenants still have not vacated the premises, you can then request the court issue a Writ of Possession. This will enable the Sheriff to retake possession of the property and possibly recoup back rent and any additional damages. The Writ must be served on the tenant within 2 days after it is issued, and will be executed on 11 days after service. I am unsure of the precise procedures Pittsburgh will use, so you will want to consult with the Sheriff out there directly.
Hope this helps!