I need to have an intelligent and collected response when finally seeing a family member over the holidays.?

I am a real estate agent, I am very experienced and have been in business for myself for almost 10 years. Well about a year ago, my cousin and his wife contacted me to help them find and purchase their first home. I was happy to do it and thoroughly enjoyed helping them. I love the excitement of first time home buyers. So over this year, I took them out many times. I held their newborn child for hours while touring homes so they would be free to look around. The areas that they were interested in were all over the island. I drove all over spending hundreds of dollars in gas and buying them lunch and coffee/snacks on different occasions. My goodwill was partly to schmooze my clients and would be HOPEFULLY paid back when the sale went through. These are the expenses associated with my job and sometimes I don't ever get money back due to the deal falling through. So about 2 months in they find out that they are expecting their next child. Ok. No problem. The search goes on right? So we go back and forth looking and nothing. Then finally we start back out touring properties and when they finally start narrowing in on a property, I insist on getting their mortgage preapproval and they start stumbling over their excuses. You see in the beginning of the search they said that they were both up for promotions and didn't want to get their preapprovals yet since their salaries were gonna change. Understandable. She is a ADA and he is a police officer and family! I am sure it I'll be fine - they are good people. So now on our 2nd leg of tours I am insisting on it and they tell me in 2 weeks they have an appt. with mortgage guy since that's their first day off at the same time. I try explaining that they could probably do all of it over phone but they want to wait. So in the meantime I contine sending listings and follow-up with them. They are planning a big party but ensure me that thy will get back on it soon. Months go by nd I finally see a posting on Facebook that thy are officially in contract on a home. I sent them an email to say that I heard the good news that they found a home and congrats. I then said that I was going to stop sending listings since it was no longer necessary and that I look forward to seeing them over the holidays. I was trying to take the high road. I got no response back. 2 months later another post pops up that they are closing on the house.

I are my job very seriously and I take my time away from my family even more seriously. I know that in my line of work, this sometimes happens... Clients just fall off the face of the earth, but this is a family member. How do you not respect me enough to waste my time like this. This was all dragged out over a year. Money out of my on pocket.... More importantly time away from my family. The fact that they did not even feel like they needed to explain or apologize after cutting me out of the sale is so disrespectful. Now, my first contact with them will be on Xmas eve in front of 60 of my closest relatives. They will probably be gushing and talking about their new home. I would love to have an intelligent and calm 'comeback' to address the situation. Can you help me to come away from this with away to say it was rude and disrespectful but look professional and 'on top'?