Assuming (and that's all we can do) for now that the second census entry might be your Margaret, then John was alive, but around 60. No sign of Jane.
There is a death on SP for a John Brown in Bothwell, age 63, in Bothwell in 1876. If he was 60 on census day and if it's the same man he would have been 65 in 1876, but then if there are different people giving the information a 2 year gap is quite reasonable.
The only other 2 John Brown deaths in Bothwell between the 1871 census and your 1811 marriage certificate are a child, and a man age 35.
What intrigues me is the age of the youngest children in 1871 against the age of the father.
It might be worth looking at that death certificate (ref is 625/01 0231) and see if it rings any bells, but before you do that and spend another 5 credits, do post what you have from Margaret's marriage.