I'm wondering what is that ligature:
The closest on the Wikipedia's list of ligatures would be "qp" but it doesn't look exactly like that.
Here is the phrase with the soluted words:
silensq(ue) sisto tuumq(ue)
I would add that this is not a ligature but an abbreviation, while -st- of the word sisto could be properly defined as a ligature.
It must be que. The conjunction -que is very common in Latin, and it is no surprise it has it's own symbol. For example suumque is (almost) the same as et suum and means "and his own". The excerpt you have is a fragment, and the exact translation depends on more context.
For me this is the Unicode Private Use Area character U+E8BF LATIN SMALL LETTER Q LIGATED WITH FINAL ET defined by a Medieval Unicode Font Initiative recommendation, however the diacritical mark over the character is a mystery for me.