You can use the ROS xacro utility to convert your XACRO files to URDF before importing into MATLAB.
In a ROS enabled terminal, you can enter the following command, replacing the paths and names for your input and output files:
rosrun xacro xacro --inorder -o ~/myfile.urdf ~/myfile.xacro
You can then check the generated file to see if it's valid
If this step is successful, you can copy the URDF file and its dependent meshes somewhere accessible by MATLAB. Then, you can try import your robot as follows
>> robot = importrobot('myfile.urdf');