Sorry to take so long to reply. There are 3 gravestones at Premnay for Tough, 3 for Robb and 6 for Stephen. There are no Maitlands. There is one that contains both Robb and Stephen, copied below. If you need any details of the others, please give me some more information.
1845: Sacred to the memory of WILLIAM STEPHEN farmer in Burry Hillock, Pramney(sic) d.21 Jan.1844 aged 75, his wife ELIZABETH ROBB d.21 Aug.1845 aged 69. ADAM STEPHEN d.Auchleven 3 Jan.1899 aged 86. Bottom: Erected by their sons
Please note that since the MIs are unpublished, they are unlikely to have been checked, so accuracy is not guaranteed. Hope that helps
MeeToo