The Sisters Hospitaller don't really get as much showing as the Battle Sisters in fluff but they are notable for being not just a military faction but a civilian one. One noted in the fluff for being very popular among the imperial population because they are willing to mission to those who could never hope to pay them back and to the dregs of society. Which is sorta where this idea came from, a few sisters (And underhivers helping them for the gangers/juves) tending to the black morass that is the underhive...and quite possibly getting stabbed in an alleyway for their medical supplies while they do it.
General Gang Design
+Skilled Champions and Leader
+Very tough, hard to actually kill off
+Exceptional Medical care.
+Good shooting skills
-Junky Juves and Mediocre Gangers.
-No heavy weapons at all.
-Mediocre melee
-Unique equipment is either expensive or not killy.
-No access to ferocity means that pinning will always be a serious issue.
General Gang Design
+Skilled Champions and Leader
+Very tough, hard to actually kill off
+Exceptional Medical care.
+Good shooting skills
-Junky Juves and Mediocre Gangers.
-No heavy weapons at all.
-Mediocre melee
-Unique equipment is either expensive or not killy.
-No access to ferocity means that pinning will always be a serious issue.