Hi Rizwana,
To my understanding, you have two points and want to calculate the Euler angles between them.
You need to do is first convert these cartesian vectors to rotation matrix and then to Euler system. Below is the brief code for the reference
% Lets take first 2 points and find Spherical coordinates.
P1 = [-426159, 501913, 845131];
P2 = [-48717.2, 499318, 847679];
v = P1-P2;
% Let's define si and theta in such a way that.
v = [r*cos(si)*cos(theta), r*sin(theta), r*sin(si)*cos(theta)]
r = norm(v);
si = atan2(v(3),v(1));
theta = atan2(v(2),sqrt(v(1).^2+v(3).^2));
j = [cos(si)*cos(theta), sin(theta), sin(si)*cos(theta)];
% Correspond to j vector you can also find orthonormal vector to j
i = [sin(si), 0, -cos(si)];
k = [cos(si)*sin(theta), -cos(theta), sin(si)*sin(theta)];
% Rotation matrix;
m = [i',j',k'];
% You can use MATLAB inbuilt function to convert rotation matrix to Euler system
eul = rotm2eul(m);
For more information you can refer to the MATALB question Euler angle from 3d points? - MATLAB Answers - MATLAB Central (mathworks.com).
Hope it helps.
