I know Mary Grant, Alexander's wife, will only be of passing interest as she is not a blood relative but I came across a mention in a book "The Chiefs of Grant" by William Fraser, vol 1, published Edinburgh 1883 in the section on cadet families of the Grants of Grant. Discussing the Grants of Kinchirdie, in particular Captain John Grant, his known children are listed. These include "Mary Grant, who married Alexander Cumming, Docharn, no issue." If that is correct, then Alexander had no legitimate children as she died after him, unless he was married before.