It is NEVER safe to assume anything in genealogy. It isn't always fast but one needs to carefully look at info at each generation and verify that it is all accurate before winging it to the next generation.

We can help you much better if you start with yourself and show us how you got back to Robert. That will no doubt allow us to determine who the wife, Catherine, is. How did you determine she was b in Arbory?

It always helps to show the info you quote.
1851 Maughold Census
01-21, 72, CHRISTIAN, Thomas, Port-e-Villyn, Head, Married, 55, Weaver, Maughold

, 01-21, 72, CHRISTIAN, Margaret, Port-e-Villyn, Wife, Married, 55, Housekeeper, Maughold

, 01-21, 72, CHRISTIAN, Ann, Port-e-Villyn, Daughter, Unmarried, 30, Emp at Home, Maughold

, 01-21, 72, CHRISTIAN, Robert, Port-e-Villyn, Son, Unmarried, 22, Labourer, Maughold

, 01-21, 72, CHRISTIAN, Ellinor, Port-e-Villyn, Daughter, Unmarried, 19, Emp at Home, Maughold

, 01-21, 72, KNEEN, Robert, Port-e-Villyn, Grandson, , 4, , Maughold (christened Robert CHRISTIAN 22 Nov 1846 Maughold s/o Ann CHRISTIAN)

, ., ., , , PAGE 22

, 01-22, 72, CORKILL, William, Port-e-Villyn, Grandson, , 1/12, , Maughold (christened William CHRISTIAN 16 Mar 1851 Maughold s/o James CORKILL and Ellinor CHRISTIAN)

, 01-22, 72, SAYLE, Margaret, Port-e-Villyn, Daughter, Widow, 35, Lab Woman, Maughold Margaret Christian md Charles SAYLE 05 JAN 1845 Bride Charles Sayle 34 Pt y Vullen buried 22 Mar 1851
Maughold Old Yard
S 45
Erected by ANNIE SAYLE in memory of her parents CHARLES SAYLE died March 14th 1851 aged 34 years
Also MARGARET wife of the above died Feb 17th 1882 aged 66 years
Also THOMAS son of the above died April 2nd 1861 aged 9 years
They sleep in Jesus

, 01-22, 72, SAYLE, Ann, Port-e-Villyn, Granddau, , 6, Scholar, Maughold

, 01-22, 72, SAYLE, Charles, Port-e-Villyn, Grandson, , 5, Scholar, Bride

, 01-22, 72, SAYLE, Thomas, Port-e-Villyn, Grandson, , 10/12, , Maughold

Thomas Christian was probably buried 14 May 1865 Maughold
Margaret was probably buried 23 Sep 1870 Maughold

Donna

Robert Christian born Maughold c1829. In 1851 he was aged 22 and living at home with his parents at Port e Vullyn.
He married a Catherine (surname unknown) who was born Arbory.
His father was a Thomas Christian, a weaver, born Maughold c1796 (55 in 1851), who married a Margaret.
BUT, who was Thomas's father?

I've had a quick look through Maughold baptisms for Thomas Christian's born 1790-1802 and found 2.

1796/2/7 Son of Wm Christian and Ann Kelly

1802/3/12 Son of Wm Christian and Margt Kerruish

Would it be reasonably safe to assume it is the 1796 record? Anyone done this family before?