Will your friends (these 2 natives) help to teach you? Would you be able to find a long-term teacher?
Would you be able to go to China?
I really don't know where to start...
If you're serious about learning to read/write and speak, the best thing is to go to China. Find a school, or get a job out there (perhaps teaching English) and find a tutor. Learn the fundamentals (tones, pronunciation, grammar, character structure) from teacher/tutor. And then of course you will pick it up by living in it.
If you can't go abroad, you will still benefit greatly from a teacher, at least at the beginning, to teach you the fundamentals. You could learn to just speak, or just read/write, but these things (tones, pronunciation, grammar, characters) are intimately connected. Neglecting any of them from the beginning will slow the progress of learning all the others, in the long run. And you'll benefit from someone to tell you where you're going wrong.
Here are some suggestions, focused a little more on reading and writing, based on my experience. Others might tell you differently, but I'm sure these things worked for me, at the beginning:
To learn the 4 tones well, you need to drill. Repetition. And someone to listen to, and to correct you. People who don't learn the tones well sound silly and have difficulty making themselves understood even if their grammar and pronunciation is perfect. Listen, repeat....
To learn pronunciation, learn pinyin. Learn the initials and finals (e.g. in "Saoshun", s and sh are initials and ao and un are finals), and practice certain difficult sounds. Again, good to have someone to listen to, and to correct you. There are some sounds that just don't make sense at first. Listen, repeat....
The grammar is mostly very simple and logical. To my eternal joy, there's no conjugation of verbs; making past/future is very straightforward. For example, (again at a basic level) generally all you need to do to make something past tense is stick one of 2 particles at the end of a sentence. As you get more advanced there are some seemingly weird structures that will need explaining, but again they're really very logical.
For me, this was the easy part, though it seems daunting to begin with.
Firstly, learn the basic character parts (radicals) and their pronunciations. You can see them here: http://zhongwen.com/
To learn the correct stroke order you'll again benefit from a teacher though there are loads of websites with animations that show you the stroke order.
Learn to write 一 and 乙 and 口 and so on, getting progressively more complex.
The radicals are generally found in combination in each character.
e.g. 妈 = 女 + 马
mother = woman + horse
Woman gives meaning, horse (ma) gives pronunciation.
If you learn all the written structures, pronunciations, and meanings of the most basic parts of the written language, the more complex parts come quite easily. Not all are so straightforward, but you can often guess at the meaning and/or pronunciation of a character if you know the components.
Then all you need to do is... repetition. To learn a character, write it out. A lot. With its pinyin pronunciation.
And with all this, of course, you need to learn the words..