Good find, Isobel. Could certainly be a brother to Allan.
With a possible clue to birth place from Donald's index, there is this index entry on Family Search:
John Mc Donald christened on 12 May 1803 at Alness, Ross & Cromarty. Parents Alexander McDonald and Betty Cameron.
When parents' names are common and likely to be more that one couple with similar names, always hard to be certain whether you are on the right line.
For example, on Scotlands People, there are a number of children with parents Alexander McDonald and Isobel/Isabel Cameron. They all show in Urquhart and Logie Wester:
James 1791
Kenneth 1793
Margaret 1795
Mary 1796
Isobel 1798
Alex. 1801
Margaret 1803
George 1806
Christian 1807
William 1809
However, no Allan (or Donald for that matter). Not conclusive as sometimes not all births & christenings are to be found...but does not help further at this time

Monica