OK, sunrays, I am going to take a flyer on this one and make a few assumptions. Correct me if I assume wrong.
First, it sounds like the new system is a pair of VFD's feeding a pair of motors that are mechanically tied together thru a common shaft. Whoever configured this system has wisely set one drive/motor as a speed regulator with the other set arranged as a torque follower. Given this arrangement, it is essential that the two motors are sharing load equally especially when at the heavy load point on the swing arc of the machine. It sounds like you have checked this but you must be sure about it.
Second, since we don't have precise torque-speed curves for the new motors we have to assume that peak torque on the motors is around 200% nameplate rating and that the current at that torque is also about 200% of nameplate full load amps. If this is right, the the VFD's must be able to supply that 200% current for as long as the overload exists. Since you said you have increased the current limit on the drives to 200% (of 125amps, I presume), it sounds like you have already anticipated this issue. However, VFD's, just like motors, have a time limit for operation at these overloads and that time limit may not be enough to get your machine thru the high-load range. A good indicator of the weakest link would be whether the drives fault when you say the system "stalls". If the drives do not fault, I assume that the motors continue to draw heavy currents, the drives drop down to near zero Hz, and the motor shafts stops turning. I wouldn't think that this condition could go on for very long before either the drives fault or the motors go up in smoke!
sunrays, if you are with me up to this point, please report back to us the output voltage, output current, and frequency of each drive when stall occurs. Also, if the drives fault when stalled, please tell us what type of drive fault occurs---ie, overcurrent, overtemperature, etc.
I'll do my best to help you thru this when you report this data for us.
Good luck.