Wardens, Sheriffs, and Constables are all offices, usually with specific responsibilities for, or over, a certain property or geographic space. It was certainly possible to possess more than one at a time, and on occasion might have been doubled up ex officio as noted here where the offices of Mayor of Conwy (village) and Constable of Conwy (castle) were specifically designated as the same official - possibly to the detriment of the latter.
Sheriff derives from Shire Reeve:
The modern word “Sheriff”, which means keeper or chief of the County, is derived from the Anglo-Saxon words “Shire-Reeve”. The Shire-Reeve, in the days of King Alfred the Great of England, in 871, was responsible for collecting taxes and enforcing the Kings Orders. The duties and the role of the Sheriff were better defined in 1215 when King John signed the Magna Carta.
Warden derives from "one who guards":
c. 1200, "one who guards," from Old North French wardein, from Frankish *warding- (which became Old French guardenc), from Proto-Germanic *wardon "to watch, guard," from PIE *war-o-, suffixed form of root *wer- (3) "perceive, watch out for." Meaning "governor of a prison" is recorded from c. 1300.
Constable derives ... from late Latin comes stabuli ‘count (head officer) of the stable’
The office of the constable was introduced in England following the Norman Conquest of 1066 and was responsible for the keeping and maintenance of the king's armaments and those of the villages as a measure of protecting individual settlements throughout the country. Some authorities place the origins of constables in England earlier, attributing the creation of the office to during the reign of King Alfred (871 A.D.).
Prior to the breakout of the English Civil war, upon which the military responsibilities would have again become predominant, I expect that most of these minor offices across England were used as sinecures for young sons, as a means of keeping them out of trouble and invested in the stability of the realm.
A regards the specific case of Ruthin Castle, its state of disrepair upon breakout of the Civil War suggests that the office might have been, whether de facto or de jure, vacant at the time until repairs were authorized.
In Volume 2 of his Memoirs of the Civil War in Wales and the Marches, 1642-1648, John Roland Philips includes two documents concerning the 1646 acquisition of Ruthin Castle:
"A Letter to the Speaker of the House of Commons, concwerning the surrender of Ruthin Castle to Thomas Mytton, Major General, ..."
The surrender terms of Ruthin Castle agreed to by both parties on *th APril, 1646.