Thanks for this. Yes I will keep an open mind and look for both Maxwell and Mackison. The Alias business is very peculiar. There are instances of both. Mackison families using the Maxwell alias that reverted to Mackison, and other families like your own that stuck with the Maxwell surname.
Mackison (or Mackessan, the older form) is a name that is mainly associated with the Forth Valley (Menteith) including the neighbouring parishes of Dunblane, Doune/Kilmadock, Port of Menteith and Callander. The Mackison/Maxwell alias occurs in every parish. These families had been there for centuries so many won't have been closely related and yet they almost all adopted the Maxwell alias. Very peculiar.
Maxwell is a name that originated in the Borders and the South West of Scotland. The Maxwells were a very powerful and landed family there.
The Mackisons in the Forth Valley were Lowlanders living very close to the Highland Line. My theory for the adoption of an alias used to be that after the 1745 Jacobite Rebellion the Mackisons wanted to make clear that they were not rebellious Highlanders which their 'Mac' surname might have suggested, so they adopted Maxwell, a name that was synonymous with Lowland Scotland. Although ironically the Maxwells were usually Jacobites! So this theory leaks!