i think you maybe need to detach yourself from the situation a bit by the sounds of your post you have actually done all you are capable of doing offering your advice (which on the employment post education note is very true in every regard) & you are there offering support wether they use it or not is out of your control. You really can't do anything more so don't cut yourself up over it - if you do feel pressure to do more it's probably best to hold back you can only offer it you can't force it.
I think your SI does sound like he may have deeper issues & professional help is the right path.
While you might not be able to do anything more than you have in that regard i'd say your daughter needs your support more than anything don't pressure her just be there for her i think just closeness without even bringing the topic of her other half into your time together would mean the world to her - while obviously it dominates her thoughts at present it must be a hard grind for her, being free of it for just a few hours would be great for her soul & bring a little peace.
But hey i'm not a professional thats just my take on it.
ABDM -
while i hear where you are coming from i'm just going to add my very brief experience on Zoloft & i am well aware that mine was a relatively uncommon scenario - but it did work very well for me.
While i didn't suffer depression, well not so much that i was aware of it although i know both are linked i did have extreme Anxiety about 10 years ago - it was fairly severe "social anxiety" so my GP put me on Zoloft. I only took Zoloft for 4 months before i stopped taking it cold turkey (not weened as GP always recommend). Within a week of commencing Zoloft my anxiety had basically dissappeared what that did allow me to do was retrain my brain once the anxiety had gone i just threw them away as mentally it had been removed. So short and sweet but while it doesn't work well for many it was the "cure" in my situation.
