Can two devices share a decoupling capacitor?
Yes it can. No problem at all. It is a common practice, group of near placed devices to have one decoupling capacitor(s).
Yes, the output capacitor of the LDO can be a decoupling capacitor for these devices, again if it is very close to them. Consider increasing its capacitance according with decoupling needs.


In all cases provide short and thick tracks for the power. The low inductance is essential here.

Don't forget that if you have electrolyte capacitor there, it have to be coupled with a low inductance ceramic capacitor.