you probably need to contact my wife Jean, her email address isVant@one-name.org
She has taken over my research into the VANTs and expanded it into a full one-name Study.
I suspect your Gt grandfather was Francis D VANT who married Ellen ROGERS in Birmingham RD in Q1 1918. (GRO ref 6d 551).
He is almost certainly the Francis D VANT that served in the Coldstream Guards in WW1, Regimental number 9091. You'll also find him in:
UK, Citations of the Distinguished Conduct Medal, 1914-1920
This is almost certainly Francis Dennis VANT who was born in Afghanistan in the East Indies in 1890. By 1901 he was living with his parents in Evesham in Worcs.
If he's yours....
Ken (son of Joan TOLL nee VANT)