James Oswald born about 1750, Wemyss

[mmkiwi]

I have James Oswald on my family tree - he was married in Wemyss to Helen Maxwell on Dec 2nd 1775.   I am trying to find James Oswalds birth - but I have 3 possibles - parents could be James Oswald and Elizabeth Wemyss who had a son James on 3/12/1751, or James Oswald and Christian Birrel who had a son James on 16/10/1748 or James Oswald and Margaret Baxter who had a son James 11/11/1750 - all were in Wemyss, Fife and found on Scotlands People.

Anyone have any suggestions on how I can figure out which James birth is the correct one? 

James and Helen had children James, John, Elspeth, Henry, Helen and Margaret so the child named Margaret may be an indicator but  .. not sure that is strong enough to get me comfortable.  As it is so far back only parish records so nothing noted to indicate a parent in marriage details.   

Appreciate any suggestions