A global point about triple stops: it's not possible to sustain them like that. Your performer (unless you instruct him or her otherwise) will arpeggiate and then sustain the top two notes or just the top note (usually top two if it's easily possible in context, as with yours).
Double stops are easily sustainable but not for very long (the player will need to change bow directions so there will be a very audible stop in the sustain - consider notating where they should change bow direction).
Can you meet with a violin or viola playing friend and try out some of these things?