Thank you very much for sharing that window into your life - and how cool that the situation between your cousin and her partner changed when you shifted to a positive and grateful frame of mind.
I'm not surprised that the situation changed - it's all vibrations, so no doubt your good vibrations influenced them.
Now, regarding what you can do to make the life of your loved ones a little better, I'm afraid there's not much you can do. You can talk to them about positive thinking, you can tell them what YOU do to change your mood, but you cannot change THEM if they don't want to change.
You say that you feel it's your duty to help them make their life better - and I can completely understand how you feel because I've been there myself, wanting to help others to see life in a better way, wanting to change them.
However, everybody is in their own path and every person is at the exact point in life that they need to be, with the exact situations they need to experience. When you start seeing it this way, your intention to change how others react to life goes away.
There is however something you CAN do - and it is easy, since it is to work on yourself. In the same way that the argument went away when you shifted to being grateful, your presence illuminates others when YOU feel good.
So the best thing you can do for yourself and for anybody is to make sure that YOU are in a positive frame of mind and deal with life's difficulties in the best way you can. Those who are ready to see your example will take something of value from it, and those who are not ready will simply go on with their stuff as usual.
That's Ok. If you want to change the world, you gotta start with yourself. You may do a lot of work on yourself before your cousin or anybody else comes up to you to say, "Hey, I've seen you always seem fine even if life gets difficult, how do you do it?" - and sometimes nobody will come up to say anything.
That's alright too. When you get to a stage where you can handle pretty much all that life gives you from a positive stance, you will see how you actually do help others with your simply being. People will feel your good vibrations, and you will definitely help others in this way.
My best advice to you: do your own work on yourself. Identify where you can do better, and get on to doing it. Have compassion for others who are not yet seeing how they can take life differently, and be open and available to them if they approach you.
Your best teaching is YOU being the example of how thinking in terms of gratitude helps to feel better.
