And a Happy New Year to you two, Monica and Ian as well as all who read this 
 
I'll try and do more on naming patterns but I need to discover any siblings of Janet Vannan.   I've found four of their children (cannot find more ):  John and the three you posted - all via SP.   Incidentally, John Bachop; Andrew Balk; Margaret Bauk and James Baulk 

    The 'ch' sound as in loch does suggest a reason for the variety of spellings.
Tobias and Janet are my 5 X greats as well.  Son John and his wife Margaret Duncanson were my 4 X greats.
I've found just 3 Tobias births in the period 1710 to 1717 - though there was a Thomas.  
10th December 1710   son of John Bachop & Helen Henderson
31st October 1712       son of Tobias Bachop & Jean Arthur
3rd December 1714     son of John Bachope & Anna Mortimer
The first was in Clackmannan parish and the other two in Alloa (Clackmannan) parish?  How do these differ please?I think I will discount the Janet born 1700.  Age 46 at marriage and then 4 children doesn't quite ring true.  Marriage at 15 (baptised 1731, possibly not soon after birth]  is OK but she married one of three men (in 1746) of  32, 34 or 36.  The youngest one perhaps is the best candidate  - for now anyway  
 
Regards
Reiver