Hi
If you are using point mass and directly connected to the base of the robot then it may also be good for your purpose because you are only interested to calculate the topple of the table when the arm would be fully stretched.
You may apply a spring with very less stiffness between the legs and the ground surface to avoid this unconstrained behaviour.
I would suggest using a transient structure to better capture the Dynamic behaviour of the robot arm and its impact on the legs of the table.
Regards,
sampat