I am not a string player so am not an expert on this practice but sometimes strings players have a way of re-articulating notes slightly even if they're the same note tied together (I heard this mentioned on the young composers discord server). In order to make it clear that you don't want those repeated quarter-note triplets re-articulated I think you might want to write them as half-note triplets since that is, ultimately their true duration (in the 2nd measure of the 2nd system on the right).