Thank you for sharing how you feel!
I'm definitely not qualified to comment on something as complex as schizophrenia, and I don't know the details of your situation, but I want to comment on a couple of things of what you said. First, I think you are dwelling too much in the "big problems": the enormous weight of your disease, your horrible experience of reality, the hard place you are in life, etc. And those things are important issues, but in my experience the way of improvement is not necessarily facing the big problems face-on, but rather to deal with the small problems you do have control over, and little by little build the competence to address the bigger ones. For instance, you said that you lack the motivation to give up smoking and drinking, implying that once you figure out life and your purpose and your place in the world, only then you will have the motivation to give up your addiction. But very often it's more helpful to see things going the opposite direction: if you put effort in improving your lifestyle, the resulting reduction in stress and the increase in the options you have for organizing your life and pursuing new things now that the addiction doesn't drag you down as much, will help you to see more clearly what you want, what you want to be motivated to do and how can you go about it. When we ponder on the dimensions of our greatest demons, we freeze; they looks so powerful and frightening that we almost lose hope the instant we see them, asking ourselves how could we possibly do something against *that*. So the best course of action, I believe, is to separate things between those which we absolutely can't do anything about, and those we can do something about, however small and inconsequential it is.
In Frank Sinatra's song, High Hopes, there are some lines which are very funny and express very well what I mean:
"When troubles call
And your back's to the wall
There a lot to be learned
That wall could fall"
If everything in our lives has gone catastrophically wrong, and unsolvable problems hide behind every corner, nevertheless it would be wise to step away from a precarious wall that may, on top of all your other problems, also crush you down. And I think having such little opportunities is something to be grateful for, and a profound meaning can be find in them. Even if everything falls apart, we can still have a little corner of the world, or a place in ourselves, or a moment of our day, where we hold on to what we hold dear. Like, if you can't defeat the MI5, then isn't it better if you go and anyways try to find joy in your day? When everything is at its worse, your effort can only possibly improve things, by whatever small and subjective amount.
Second, I'm sure your parents appreciate the small gestures of kindness you offer them. I'm sorry for getting religious, but there is a Bible passage that explores wonderfully this subject: "Jesus sat down opposite the place where the offerings were put and watched the crowd putting their money into the temple treasury. Many rich people threw in large amounts. But a poor widow came and put in two very small copper coins, worth only a few cents. Calling his disciples to him, Jesus said, “Truly I tell you, this poor widow has put more into the treasury than all the others. They all gave out of their wealth; but she, out of her poverty, put in everything—all she had to live on”" (Mark 12:41-44). I'm sure your parents understand how much you struggle, and how hard it is for you to give kindness even to yourself, and that makes your actions even more sincere and brave. If a person who has had it easy on life, and doesn't have any problems, and is joyful all the time, gives you a compliment, that compliment it's almost banal, superficial. But the love which rises against all obstacles, that's very valuable.
And if I'm honest with you, I don't even remember the last time someone gave me flowers, nor I remember the last time somebody else I know received flowers. So really, don't underestimate how moving small but sincere gestures can be.
I hope something of what I said may help you even a little. Let me tell you from the bottom of my heart that you are a valuable person and I wish you all the happiness in the world.