In order to successfully load multiple Libraries, you must learn to use the LOAD Type "1 Bank Voice"

Please see the following article on the MOXF Flash Board

Loading "1Bank Voice" instead of using Load Type = ALL, this will let you select, where to place the Voice data that supports the Library Waveforms. Take the first Bank and load it to USER1, take the second and direct it to USER2, and finally the third to USER3.

You need to count up how much Sample memory you are going to be using, how many Voices you will be loading.
If you have more data than fits on your Board (sorry that you did not mention the size Flash Board, nor did you mention the size of those Libraries), or if you have more Voices than fit in your three User Banks, (you also don't mention the number of total Voices in these Libraries).

The FL512M allows 510MB of Waveform/Sample data, 384 Normal Voices
THE FL1024M allows 1022MB of Waveform/Samples data, 384 Normal Voices

Add up your total amount of Waveform/Samples and the recognize that there is room for 3 Banks of 128 Normal Voices at once on your Flash Board.
There is also a limit of 2,048 total Waveforms, 8,192 individual KeyBanks

You will be out of memory as soon as you exceed any of these limits.

Reassembling the Performances and/or Arpeggiators is another story, let us know what you're dealing with, that is, the nature of libraries you've mentioned.