The Clan Stewart of Appin did not appear until about 1497, when Dougall McLaurin of Ardveich, Strathearn, took Appin by force of Arms and formed the Stewart of Appin Clan. Dougall Mclaurin was Stewart of Appin 1st.
Your second paragraph contradicts the first paragraph.
Rob Roy did not participate in an almost Clan battle, nor did he fight an Alasdair Stewart. The property in question Wester Invernenty was disponed to Duncan McLaurin by John McLaurin, Baron Stobchoin in May of 1736. Rob Roy's youngest son Robert in retaliation murdered John McLaurin later in 1736. Rob Roy died Dec. 28, 1734 over two years before the property dispute.
There has been great controversy on the name "MacLaren" being placed on the "Appin Regiment" Marker. There were twenty-seven Appin mclaurins who fought in the Appin Regiment, they had lived on the various Appin Estates since the early 1500's. The fourteen survivors names are documented in the Stonefield and Saltoun manuscripts each almost duplicating the other, so a double confirmation. "John of Culloden" from Glen Creran Appin, was killed at Culloden according to the oral tradition, we have no record of the Appin McLaurins who died at Culloden. Duncan Mclaurin of Blar-nan-laogh, Glennahyle is the Appin Mclaurin that received the sword cut to the face. Duncan is in both Saltoun and Stonefield lists. As far as i know, no Appin Regiment Muster Rolls exist, they weren't really mustered, most were probably forced into service.
There was no Balquhidder MacLaren Company lead by Donald Maclaren of Invernenty in the Appin Regiment. All Appin Companies which were lead by the Appin Estate owners are accounted for in "The Order Book of the Appin Regiment" which is available from the National War Museum in Scotland. On the contrary all contemporary accounts of the Balquhidder MacLarens place them in the Atholl Brigade, except Peter McLaren of Muthill and malcom McLaren of Invernenty who served in the Edinburgh Comapny under John Roy Stewart a professional soldier. I have copies of letters to and from Donald Mclaren the Drover of Invernenty from Grigor Murray placing him in the company of John Roy Stewart, Colonel of the Edinburgh Regiment. One letter states very clearly that Donald was to meet Grigor Murray at the Kirktown of Balquhidder to Muster men from Balquhidder, Glen Almond and Strathearn for the Atholl Brigade at Duke Murray's request.
After Culloden, Donald MacLaren the supposed leader of the fictional MacLaren Company was captured in the Braes of Leny with an Officer and other Jacobites from the Atholl Brigade. Donald's brother Duncan of Invernenty was a Lieutenant in the Atholl Brigade along with six or seven other Strathearn Maclarens. This is well documented from newspaper accounts of the capture and President Forbes.
The only missing piece is any evidence to support the claim that Balquhidder MacLarens were in the Appin Regiment. It is a shame that MacLaren of Maclaren and the Clan MacLaren Society have desecrated the memory of the Appin Mclaurins who actually fought and died at Culloden. Especially since the above writer "Tuirc" ancestors were in the Appin Regiment. His ancestors uncle was the above Duncan McLaurin who was severely wounded in the head.