I have been working on a Wilkinson equal power divider. Most of the S matrix looks fine but the two output match is very poor, only -12dB or so. I have defined a RLC lump boundary for the 100 ohms resistor. The layout of my Wilkinson is attached. Please take a look and comment on why the output match is so bad.
Your input legs are not constant impedance lines. All three legs going into your Wilkinson should be 50 ohm microstrip lines (assumed because you stated you used a 100 ohm load isolation resistor). I'd recommend taking your input lines straight up and down, then go into optimal 90 degree bends, so they are square to the board edge.