Hi Julie, ScotlandsPeople (
https://www.scotlandspeople.gov.uk) is the key to your Scottish research.
Your Thomas McLaren has a baptismal record there, May 15th, 1831 in Kilsyth, parents are Robert McLaren and Janet Gracie. The index to the records is free, the actual image costs a few dollars.
Sometimes there is no baptismal record, or it's hard to find because the name is spelled differently or some date is off. I find the death records are also very good in Scotland because they usually name the parents as well.
For example, there is no 1883 birth record for a Matthew McLaren but one of the Matthews was born in St Andrew (Dundee) in 1885, There is also a William McLaren born in St Andrew (Dundee) in 1897, so that is consistent with his profile and perhaps suggests that the Matthew in 1885 is the other brother.
There are 2 death records for a Matthew McLaren in 1935. Which one is Thomas's son, I'm not sure. You'd have to pay to see that record.
Hopefully, that's enough to get someone started!