Yes, I can see that John Bletsoe married Mary Darling at Rushden, and that they baptised five children there: John, Martha, Ann, Thomas and William. After William in 1759, there are no more Rushden baptisms for children of John and Mary, although it seems that they lived until 1771 (John) and 1781 (Mary).
Charles and Timothy, who were born c1770 and c1771 respectively, both name Rushden as their birthplace, but seem not to have been baptised there. These two are definitely brothers, as Timothy names Charles as such in his will.
Thomas Bletsoe of Easton names siblings Charles, John, William,Susannah, Kezia and Timothy in his will of 1806, but there are no addresses given, and as there appear to be a number of Bletsoe families spread across the Hunts/Northants/Beds borders around the late 18th and early 19th centuries, I don't feel that I can be certain that Thomas of Easton and his siblings are definitely the children of John and Mary (although I would like them to be).