Overwatering and underwatering can often produce very similar symptoms. The signs of leaf spot on the nandina and the dropping of lower/interior foliage on the Indian hawthorn (a very drought tolerant plant) would lead me to guess these are being overwatered as opposed to under.

But it is impossible to tell for certain without checking the soil and preferrably to the depth of the rootball. The soil should be loose and free-draining and be allowed to dry slightly between waterings. It should feel just barely moist - not wet - to the touch.