The IGI has an extracted marriage entry for Peter Ferguson and Catherine Mclaren 16th July 1814 in Kilmadock, Perth.
Is this your couple?
There is a possible family in King St, Auchtergaven on the 1841 census, with Peter 65, Catherine 60 and Janet 25, also several other Ferguson females who could be further siblings or wifes and children of John and James?
There are so many Fergusons with these christian names I think you might need more details to narrow them down.
Kirsty