I've just done some checking with the IGI. My William Gillespie was baptised in Paisley & his parents are shown as William Gillespie & Jean Mair. However, there is also a William Gillespie shown who was born 11 Jan 1819 in Denny to Andrew Gillespie & Mary Smith. Andrew & Mary were married 23 Jan 1818. A parent search on Andrew & Mary shows, in addition to William: James b. 1820, James Smith b. 1830, Mary 1832, George 1840, Jane 1842, Elizabeth 1834, Janet 1828. These are all extracts so should be fairly reliable. There is no Robert but there is a Robert listed in 1826 as the son of Andrew Gillespie & Margaret Smith. This is also an extract so it looks as if it could be a mis-recording. These look most likely for your family.
B