GR translation: the elder Dr. Groast

[Mike Jing]

 “It is part,” Rollo writes home to the elder Dr. Groast in Lancashire, in
elaborate revenge for childhood tales of Jenny Greenteeth waiting out in
the fens to drown him, “part of an old and clandestine drama for which the
human body serves only as a set of very allusive, often cryptic
programme-notes—

Is the elder Dr. Groast Rollo's brother?