If it is occupied there is a chance that it will take a very long time to get possession. 

It sounds awfully easy to get the previous owner out.1 - A Writ of Possession is required to legally remove them.

@Roger Gelpey, it is my opinion, and that of some experts, that you can quiet title if you have a tax deed and you are in undisputed exclusive possession. 

Usually older houses will already possess good-looking trim that can simply be retouched to look as good as the day it was made.

The 21 year interval mentioned is the time period for "adverse possession" in Pennsylvania; failure to serve notice would result in this situation.

I has been my understanding that once the bank takes possession, they have a pretty strait forward system of getting them back to market.

You likely need to serve notice (which can be done in some cases before you close) then you need to wait the required time and then you can get possession or have the sheriff escort them out of your property.

Legal issues and other circumstances have led to my family holding possession of the property despite most of the demolition having already occurred.

This takes a while so you may want to get that started before the 30 days is up.Order a lien sheet to see what bills are due for you to record you deed.Record you deed.If it is occupied you either need to do cash for keys or file for a writ of possession.

You need a judgment to get possession of your property.