No no no and no my friend.
First of all, you are not vegan if you eat cheese, or drink milk. You are vegetarian, and this can be an okay diet.
Then let me explain it to you.
Your brain need 20 essientals amino acids to work, develop, and accessorely not die.
You Can product 12 of them on your own, the 8 others need to be found in the nature. They all exist on the vegetals reign, except for B12. B12 is naturally product if you are a vos or any ruminants. You Can find it if your specie eat its own poo, like rabbits. But if you are a carnivorian, a scavenger, or if you cant eat your own poo like humans, dog, Cats... Then you need to find it.
And you Can only find it in products that Come from other animals like meat, eggs, cheese and milk in enormous quantities.
And these pills are made with the help of animals, it IS not fully synthetic.
So you can't be a Real vegan. You can go vegetarian but the best will be flexitarian, a bit of everything.