On familysearch.org, fathers baptising children at Stanhope between 1700 and 1740 are Thomas, (5), Lowinger, (2), John, (3), and Anthony, (2).
No Stephen for any of them unfortunately, but you should really check the original register, as it is not unheard of for entries to be missed out, or unreadable, or mistranscribed, or there may be no entries at all for some years, either because those pages are missing for whatever reason, or lost, or there was no vicar at the church for some of the time.
Unfortunately, the St Thomas registers are still only on film on famiysearch.org, so you may have to wait until they are digitised, (they were supposed to have digitised all their films by 2020, so they're running a bit behind!), or visit the Durham record office to look at them
Film number 7939680 contains a printed book of marriages at Stanhope.
The marriage of Stephen and Jane Walton on May 12th 1756 has witnesses Joseph Barnfather and Nicholas Barnfather.
There were 5 marriages recorded that day. Another one was for a Thomas Barnfather and Ann Watson. Their witnesses were John Richardson and Thomas Watson.
It may be that the Barnfathers who witnesses Stephen Maddison's marriage were already at the church for the Barnfather marriage, and stepped in as witnesses, or they may have been friends or neighbours, or related in some way.