What is the ruling on one partner in a business contributing less than his two partners without informing them, and what are the implications of that?

What you did by making your two colleagues believe you paid the same amount they did is a mistake and deception, and you must inform them of it. If they consent, there is no blame. Otherwise, you must return the excess amount to each of them, because the wealth of a Muslim is not permissible except with his willing consent.