Ok - bear with me for the background to this one.
When I was just eighteen, my mom died in a car accident. Grieving and adrift, I decided it would be a good idea to quit school (community college, not high school) and move 3 hours to OtherCity to get an apartment with my long-distance boyfriend, whom I had only been together with for a few months. He was still living with his parents at the time, and the plan was that I would stay with them for a month or so while I got a job and then we would move out.
His parents were luckily much wiser than we were, and I ended up living with them and working for a year (BF was working as well). His parents sat us down after that point, and asked if we wanted to go back to school, in which case we could live with them until we finished. Not only did they encourage me to go back to school, they paid for my associate's degree as well. Once I had that degree and went on to a four-year college, they supported me in numerous ways, financial and emotional. BF and I got engaged, he graduated, and got a job.
Then... things fell apart. Fiance struggled with physical illness and was eventually diagnosed with a severe anxiety disorder that needed significant medication to control. He lost his job, and for the three years after that, did not work at all. He spent most of his time either driving aimlessly around or playing video games. His parents paid all his bills and he seemed to have absolutely no problem spending their money, living in their home rent-free, and using me as a co-dependent emotional crutch. He either could not or would not do what was necessary to control his anxiety - I'm still not sure to this day which it was. I moved out of his parent's house when it became clear he would not or could not; I had lived with them for six years by this point. Eventually, after three years of deeply unhealthy relations between us (and eight years overall) I ended the rel@tionship. Ex-fiance spiraled out of control and handled it very, VERY badly.
The thing was, while I did not mourn losing him, I lost his parents as well. I love them as deeply as my own parents. It is no exaggeration to say that they made my future possible. I owe everything I am and everything I have to them. When Ex was out of control after our breakup, in an attempt to help him, his mother made clear that although she loved me and would miss me, her first priority was to her son and she could have no contact with me lest it look like she was choosing me over her biological son. I understood completely, and despite how wrenching it was for me to lose a mother a second time, I respected her wishes entirely.
Now, it's been over a year since this all happened and I have moved away to another city and am finishing my first year of graduate school. I have had absolutely no contact with Ex or his parents during this year. I hear from third parties that Ex is doing better, working and d@ting, but still living at home. Here's the thing - I want to contact his parents. I am not trying to re-initiate a rel@tionship with them, but I feel like in the chaos of my leaving, I never expressed my extreme gratitude for both the financial and the emotional gifts and support that his parents gave to me and it weighs heavily on me that I accepted all of this help from them and then disappeared without so much as a "thanks". I would never have gone to college at all, let alone be capable of fulfilling my dreams in graduate school, if it wasn't for them.
However, I'm not sure I can separate this desire to thank them from my very real and intense missing them, either. I miss her as much as I miss my own deceased mother, and I miss him as much as I would (theoretically) miss my own father. As far as Ex goes, I do not miss him at all and in fact do not want any contact with him whatsoever. I wonder if this intense urge to say thank you is also partially motivated by my longing for them and I'd like objective opinions. So - thank you for making it this far, on to the questions:
A. Is is inappropriate for me to contact them at all? I would make very clear that I do not expect or need a response, and that I'm not trying to barge my way back into their lives, but maybe even with that caveat it's still not okay for me to contact them.
B. If it would be okay to contact them, how? I feel like a phone call would be inappropriate because it puts them on the spot - and plus, what if Ex answered the phone? Ex's mother is on Facebook, so I could send a message over FB, or I could send a letter or a card. What would put the least pressure on them and be the most appropriate?