Link with multiple parent or multiple joint with same child

I need to connect four links(below each link there is a motor, i.e actuated joint) all together to a single big square link, so I needed to model four joints(no actuator attached to them, free), with each joint having the same child(which is the big square link), but after running the simulation in Gazebo, the model was not stable and I could not actuate other joints which were supposed to lift up and down big square link. So my very basic question for starter here is, is it possible to have multiple joint sharing the same child (or parent, if the difference matters) ? If so, what parameters should I include in sdf modeling to keep it stable. Here is a small chunck of my sdf modeling: 1-0.06573 -0.000135 0.235000 0 0 00.50.0021105379831454386.068160057964515e-065.782219040307764e-050.0025371464552802047-3.9203677986423195e-060.0030817843064528650.14 0.14 0.12model://my_tracks/meshes/Body.stl0.4 0.4 0.4 10.8 0.8 0.8 10 0 0 00 0 0 10.04073 -0.05200 -0.065 0 0 0aaly__thigh_right_frontaaly__body1 0 0-0.04573 -0.052 -0.065 0 0 0aaly__thigh_right_backaaly__body1 0 00.04073 0.05200 -0.065 0 0 0aaly__thigh_left_frontaaly__body1 0 0-0.04573 0.052 -0.065 0 0 0aaly__thigh_left_backaaly__body1 0 0 I'm using ROS Kinetic with Gazebo 7.0