Hey Cutaia,
I have been in a few bands these last five years and currently play in a cover band I have been with going on 2 years. I don't think anyone in the band is versed in music theory. I also don't believe any of us can read music, let alone sight read. That being said, we all can learn songs by ear and certainly are versed in the names of notes and chords, etc. My band mates are fine musicians, despite our lack of theory knowledge. That being said, I think having that knowledge is helpful and a plus, but definitely not necessary. Some of the finest players I know can't read a note and some players with more music theory knowledge than I could ever hope to know, are not very good players.
My advice is to jump in. The key to a successful band is not being versed in music theory. It is being able to get along with your band mates and avoiding drama. Each player will have strengths and weaknesses. As long as you can play off of each other's strengths and weaknesses you are half way there. The other half is devotion to the craft. We practice once per week and each of us spends much time learning the songs at home before practice. Each member comes to rehearsal knowing there parts from working at home and we refine it, as a band, at rehearsal.
It takes alot of devotion to have a successful band. Knowing music theory, while a good thing to know in my opinion, is not necessary to have a successful band. Personalities and devotion are the keys. If it is your passion ... jump in. It has always been my passion, yet it was not until my wife surprised me with a trip to Rock 'N Roll Fantasy camp 5 years ago, at age 47 that I first really played with other musicians. It convinced me I could do it. I came home from the camp and put my first real band together. That band ended due to drama, not music knowledge. I then put other bands together and couldn't be more pleased with my current band. We gig about 1 to 3 times a month and all share a passion for playing music.
Though I would love to do originals, I satisfy that part of my passion by recording music on my own.
Good luck,
Dave