The most commonly accepted version of the origin of the McElhiney/McAlhany/McElheny (and hundreds of other variations on the spelling) name is as follows:
It is a contraction of the Celtic name Mac Giolla Eannagh, which is literally translated as "Son of - a follower of - Eannagh"
The most likely candidate for Eannagh is St. Eanna, an early Irish Christian who founded abbeys and churches throughout western Ireland, particularly on the Aran Isles, worked with St. Columbkill in county Donegal, and later founded the Christian community at Iona off the coast of Scotland.
There was much traffic between Ireland and Scotland, and I too have heard of the association of the McElhineys with the Campbells.I suspect that the McElhineys originated in Donegal, but some emigrated to Argyll where they became clients of the Campbells.Others went to Ayrshire.Both groups would have become Presbyterian at the time of the Scottish Reformation, and in the early 1600s would have taken part in the colonization of the "vacant" lands in Ulster, perhaps as part of the Cunningham plantation.
This may explain why there are both Protestant and Roman Catholic McElhineys in county Donegal.
Some McLaine families may be distantly related, but it wouldn't be a close relationship.