You should be able to relatively simultaneously. You can use either hardware or software triggers. If the instruments have a trigger input, then you can program them to take a measurement when the external trigger event occurs. If you don't have a method to generate that trigger event, then a software trigger might work. GPIB supports the Group Execute Trigger and this function can be found on the Instrument I/O>GPIB palette. I say relatively simultaneous because there's always going to be some delay between the receipt of a trigger and the measurment actually being taken. You'll have to determine what is actually meant be simultaneous and whether the instrument's specs are good enough.
