You should create 3 lines, one appartaining and controlling each DAQ (create channel, read channel, etc). If you put them in 3 different while loops, then you can visualize simultaneously the results.

Regarding the synchronization part, here's a link from NI which explains step by step how to coordinate various devices:

http://www.ni.com/product-documentation/4322/en/

It is pretty simple the cards used are different. In the block diagram use individual initialisation and take data in parallel depending on your condition. Make some process or condition where the inputs are from these three cards. It will take data almost simultaneously.

In attached file you may find an example of how I synchronize two blocks: NI-9263 (AO) and NI-9205 (AI). I use it for my voltage-capacitance (CV) characteristics measurement setup. At least it works fine for me. I hope that will be helpful despite that I anwer with such a delay. p.s. I do believe my method is not true enough and by the link suggested earlier you may find a more correct way, but my method is pretty simple. The example was created with NI LabVIEW 2016.

Best regards,

Dmitrii