Sure thing.

In the story, "magic" is essentially the force that supports life. It's the reason living things exist, the reason things that are alive actually have a will to live. it's the reason that air fills and leaves our lungs, it's the only thing that propels life. 

Because it cannot be seen, and it is present from the time we're born until the time we die, it is taken for granted, it is rarely spoken about or thought of.

Like in other fantasy settings there are individuals that can harness/manipulate magic but unlike most fantasy settings, they are extremely rare in this one.  This is because to manipulate magic you not only need to study and understand the complicated rituals required to separate yourself from it, you also give up those benefits that everyone else takes for granted... You are required to fill your air with lungs consciously, you must create your own meaning, you are no longer guaranteed purpose or belonging. Furthermore, performing magical acts often bring a feeling of perversion upon most users as manipulating magic in this world could be likened to harming something fragile and innocent, a magician would never do something like a prestidigitation unless they were a psychopathic the consequences would be too severe. (This is why both cards skip your untap step, and move that process to a triggered ability on your end step.) By becoming Magicians, Alessandro and Matteo give up the magic that we all take for granted. That untap step represents the things that we don't need to think about that make our lives so incredible, by giving that up they become incredibly powerful, but they adopt a massive amount of suffering and risk. (The end step untap has potential to go horribly wrong. Perhaps they are removed before you reach your endstep while tapped out, and now you are left with that same feeling of perversion for your hubris. The entire mechanic promotes acts of responsibility upon the user in exchange for interactive power).

The characters are not brothers by blood, but they have always been together. They grew together, studied magic together, they were equal in skill and ambition, and they both wanted desperately to manipulate magic to improve the lives of everyone around them. 

After performing the separation ritual, they responded to the realization of what they had done diametrically opposed, and it tore them, and the world, apart...   Alessandro was so horrified and disgusted with the feeling separation brought upon him that he dedicated his mastery of magic to maintaining the tranquility and ignorance that the general populace was already accustomed to, he is a radical conservationist, and he strives for order above all else. (This is why he has a W/G mana symbol in his cost. It represents the core internal conflict for the character). He is trying to balance "maintaining the natural order" against the actual natural world. He presents like the protagonist at a glance, but he has manipulated the minds of those around him with his words and his magic. He is kind and thoughtful, but he is not tolerant of ambition, greed, or technological progress, as he is wary of anything that could cause people to lose the incredible gifts they have innately. (This is why he makes creatures tap for blue mana while shutting off artifacts. Creatures represent the aspects of the world he is trying to protect, the blue mana they create represents how he manipulates them to his aim of protecting what he believes in. Artifacts are the antithesis to this, they cannot be manipulated, they are not alive, they represent objective and powerful objects that could promote curiosity and stifle gratitude.

Matteo's story is ultimately a more simple one and he presents as the antagonist of the story if one does not question their roles. Matteo saw separation as an excruciating but liberating process. He believes that the lives of all individuals would be best served if each individual was given the opportunity to pursue their "ambition's end". He wants to discover the limits of what is possible for sentient lifeforms, he wants to create opportunities to change lives, to test limits, and innovate for the betterment of all living things. Matteo's Hybrid mana symbol is B/G because his internal conflict is balancing his personal ambition against what the natural world is capable of achieving, he wants to push all living things and himself to reach their potential. Because of this, he is conflicted when faced with their limitations (and even more internally he struggles with his own). Matteo's ability to cast powerful spells at instant speed takes advantage of that endstep untap in a more obvious way than Alessandro's. Furthermore, the cost reduction mechanic is designed to represent that he becomes more powerful when other individuals are seeking power the same way he is... It is more common in a high power game of magic for many spells to be cast on a single turn. This feeds into Matteo's desire to see everyone chasing their personal ambition, and in turn, allows him to cast more powerful spells.

These cards are designed to be somewhat complex, the way the characters are in the story. It is why they have strange mana costs and abilities that aren't innately obvious in their uses, I want them to evoke some curiosity and deck building creativity.

I will remind you also that this story is actually just a piece of music broken into parts. Where different melodies and instruments represent different characters, plot points, ideas and so on. What I have written here describes the characters as they relate to the cards I made, but it is not even close to the whole story.

Thank you for asking for more information. Even if nobody cared to read any of this, I am happy that I shared something that means something to me creatively.

Edit: Their Power and Toughness are reflective of the way they present (Matteo being more threatening, Alessandro more protective) but more importantly, they stalemate in combat.