If it is just some of the lower leaves on each stem that are shriveling and falling, don't be alarmed; Jades do that periodically.
If the leaf drop is more extensive, then the shriveled leaves mean that they are not getting enough water. A weekly watering may actually be too much water. If the roots are kept in constantly moist soil, they will rot. When roots rot, then the stems and leaves have no way to get water, so they shrivel. Always allow the top third of the rootball to dry before watering thoroughly. That often takes more than a week.
If you repotted your jade into a larger pot, that may be contributing the root rot.