The identity of James Harris (28) is fairly well established including his baptismin Dodderhill.
The baptism register gives James' parents as William and Mary Harris resident in St Nicholas Droitwich.
When James and Christiana married James was a Bricklayer.
James is not with his parents in the 1841 Census.
There are several William Harris and Mary in Worcestershire around this time, but only one in Droitwich where James was born.
Thus the marriage of William harris to Mary Harrison looks most likely but has no supporting evidence.
Several potential baptisms have been identified for William.  One of these looks most likely but gives the surname as Harrison.

Therefore the identity of William and Mary as James' parents is fairly certain.
His earlier identity is uncertain as yet.
  

Willm. Harris			12 Aug 1784		CASTLEMORTON,WORCESTER,ENGLAND	Austin Harris, Jane
William Harris			10 Jan 1784		Overbury, Worcester, England	John, Mary
William Harris			20 Jun 1784		WELLAND,WORCESTER,ENGLAND	Thomas Harris, Sarah
William Aston Harris	10 Mar 1784		Charles Harris, Catharine
William Harris			08 Apr 1786		Church-Lench, Worcester, England	Hannah Harris
William Harrison		06 Aug 1786		DODDERHILL,WORCESTER,ENGLAND	William Harrison, Ann
William Harris			20 Aug 1786		ECKINGTON,WORCESTER,ENGLAND	Samuel Harris, Mary
William Harrison		12 Jan 1787		KIDDERMINSTER,WORCESTER,ENGLAND	John Harrison, Ann
William Harris			18 Mar 1787		ALVECHURCH,WORCESTER,ENGLAND	John Harris, Sarah
William Harris			28 May 1788		WELLAND,WORCESTER,ENGLAND	William Harris, Sarah
William Harrison		14 Feb 1789		Dodderhill, England	Edward Harrison, Elizabeth 
William Harriss			06 Mar 1789		Bromsgrove, Worcester, England	John Harriss, Mary
William Harrison		22 Nov 1789		Dodderhill, England	George Harrison, Elizabeth 
William Harrison		02 Oct 1789		Bromsgrove, Worcester, England	Thomas Harrison, Mary
William Harris			25 Oct 1789		Castlemoreton, Worcester, England	Austin Harris, Jane Harris
						
According to the 1851 Census William was born in Droitwich in about 1787, this would include Dodderhill.
There is thus one of these that is by far the most likley, but the parents are named Harrison not Harris.
  

If the parents of William were William and Ann then the following are probably his siblings.
Baptisms at St Augustine, Dodderhill to William and Ann Harrison/Harris.
1780-02-20	John Harrison		In Liberties
1782-01-12	Mary Harrison		In Liberties
1786-08-06	William Harrison	Pauper
1789-06-20	Ann Harris			In Liberties