I would think your John MacDonell and Janet MacDonald came in 1786 on the Ship MacDonald from Knoydart. The UEL were given lots along the river and later the ones from Knoydart were settled mostly in Lancaster and some in Charlottenburgh.
Almost all lots given in the 6th of Lancaster went to Knoydart people. For some reason Lot 32 and Lot 33 are missing from the list. Lot 34 had a Ranald MacDonald & Lot 35 John MacDonald.