They ascend to become Gods which is somehow not contradicting the monotheistic aspect of Christianity.
I don't think adherence to a rigorous definition of "monotheism" is really necessarily a premise of Christian belief. Every mainstream Christian denomination has thought more carefully about this definitional issue than any of us here have. If it's important to you, there's a menu of mainline denominations to select from to calibrate your "monotheism" to your church's.