Hi Gillian ,
On manxbmd.com there are two marriages for Thomas Phillip Collister
1912 Parish of Arbory , married in Malew ref 300 25 COE
1928 Parish Knock-E- View , married in Malew , ref 425 4 COE.
But the 1912 does not match with Catherine/Kate Callow , and 1928 does not match with Ann Duff
Appears Howard was born 1926 as William Robert Howard Duff.
Cheers
David