I've noticed that people sometimes talk as if Leibniz's monads were not spatiotemporal objects. But that seems to me to be just like saying that physicalist reductionists don't believe in mental states. The physicalist reductionist believes in mental states—she just thinks that they are nothing but physical states. Similarly, Leibniz believes in spatial relations between monads—he just thinks that they reduce to the clarity and confusion of conscious and, especially, unconscious perceptions. We shouldn't confuse the reductionist with the eliminativist.
Things are less clear with regard to causation, because Leibniz quite often talks about how there is no causation between monads, and yet he gives what seems to be a reduction of causation between monads to explanatory relations between intra-monadic states. One reading of what's going on there is that Leibniz himself recognizes that his reduction is unsatisfactory, and hence that this is only a causal-like relation rather than real causation. It may be important to his view here that the is a meaningful distinction between this quasi-causation and genuine causation, because in his system there is a place for each: genuine causation occurs within a monad and between God and a monad (I'm stipulatively using "monad" in a way that excludes God; I am not clear whether Leibniz would call God a monad; he has one passage where he referred to God as a monad and then crossed it out), while quasi-causation occurs between monads.