You need to find two points' co-ordinates here. let these points' co-ordinates be denoted by C and D.
let the 2 given points be A and B.
to find C and D, you can take variables for C and D coordinates and then take them as the mid-points for A and D, C and B, respectively. you will get equations, solve them, and get the answer.
there's a second method and easier one.
the 2 points C and D divide the line segment into 3 equal parts. C divides the AB in ratio 1:2 and D divides AB in ratio 2:1.
putting the line segment ratio formula in straight lines, you can solve for C and D.