Well we do not know how the titles were created in this specific case and often wedding contracts in which both bride and groom were titled had provisions for splitting tiles and inheritances between sons (see the Nevilles)
We do have a pretty clear picture that most titles created by Letters Patent (which was usual after the late 14th century) had a remainder to the heirs male (either of the body of the holder or simply heir males)
Wedding contracts were property agreements they did not dictate the succession to a peerage title that right rested entirely with the sovereign in the English system.
Yes you can specify that the lordship of manor a and your best bed goes to daughter a, and manor c goes to son d - but your hereditary peerage titles passed to your legal heir unless they'd been specifically disbarred from inheriting for example they'd been found to be illegitimate.
What do you mean by the Nevilles splitting inheritances and titles??
Please elaborate which titles - because the titles held by the Neville family were -
Earldom of Westmorland passed to the senior male line descendants of the 1st Earl as was usual
Earldom of Salisbury - was held by Richard Neville ( a younger son of the 1st Earl) in right of his wife - though unclear if a new title was created at this point for Richard - either way it passed to his son the Kingmaker and then went into abeyance as there were multiple claimants - was created as a new title for George Duke of Clarence and extinct at his attainder, was granted as a new creation for Edward of Middleham again went extinct. It was restored for Clarence's daughter but is unclear whether the restoration was that of the Earldom created for Clarence of the original Montacute creation of 1337.
Earldom of Warwick - again held in right of his wife (the 16th Countess) by the Kingmaker - technically his widow remained the title holder but a new Earldom of Warwick was created for Clarence extinct on his death and recreated as a new creation for his son in 1478 (probably because the boy was the likely heir of his grandmother)