Alison, have you considered the possibility that your relatives were Roman Catholic? There was and still is quite a strong RC congregation in the Tomintoul/Glenlivet area, and this might help to explain the low level or recording of baptisms and marriages.
Roman Catholic records for that area have survived from the 1800s onwards, but not from the 18th century. The Statistical Account of Kirkmichael (written by the Rev John Grant in 1791-3) says that the parish contained 1276 inhabitants, of whom 384 were Roman Catholics. The reverend gentleman evidently resents the influence of the RC priest, complaining that "the priest generally takes the liberty of sharing in the functions that belong to the Protestant clergyman". He adds, in a footnote, that there will consequently be several marriages and baptisms unknown to the Session and hence not in its records, and he goes on to congratulate himself is being so tolerant as to have allowed the RC priest to "marry and baptize, impose penalties, and exact them among his own people, in the same manner as if he were of the Established Church".
Later on he writes, "The common idiom of this country, is a dialect of the ancient Celtic .... The young people speak Gaelic and English indifferently, and with equal impropriety .... Some of the old people speak the Gaelic, and consequently with a degree of propriety".
In the New Statistical Account of 1834-5, the Rev Alexander Tulloch writes, "The language generally spoken is the Gaelic, but it has decreased very considerably in the last forty years. There is no an individual between twelve and forty years of age who cannot speak English. They all read English, and there are many of the rising generation who cannot speak Gaelic". In that year there were 1722 people in the parish, of whom 485 were Roman Catholic.
So I think you can be pretty certain that your own 18th century ancestors in Kirkmichael did speak Gaelic, and it is likely that they still did so in the 1830s.
In fact, if you are interested in the social and economic background to your ancestors' lives, I stongly recommend reading the relevant Statistical Accounts. These accounts were written for each parish by the minister, and some of them, of which the Kirkmichael one is a shining example, digress into all sorts of related and even some unrelated matters which are highly entertaining as well as informative.
The Statistical Accounts can be read online at
http://edina.ac.uk/stat-acc-scot/. You can browse them without being a subscriber - the browse link is at the foot of the page.
