OK, this is going to be a little bit of planning and work. Here are some preliminary tasks you need to perform:
1. How much space is left on the 128 gig SSD in the newer MacPro? Let me tell you my situation, so that you can get an idea how many applications you can "migrate" from the old MacBook Pro to the newer one.
My MacMini has a 256 gig SSD, and my MacBook Air has a 251 gig SSD. In addition to version 10.11.3 of El Capitan, I have the following 3rd party applications installed:
1Password
Onyx
Office 2011
Quicken 2007
TechTool Pro
SuperDuper!
VLC
Easy Find (a replacement for Spotlight)
Transmission
Trash It!
AppCleaner
Google Chrome
Firefox
Klondike Forever (a solitaire game)
Magic Number Machine (a calculator)
altMonitor
Adobe Acrobat Pro
I have a few more smaller ones. I also have in my Documents folder some other personal stuff, including two folders that contain both original applications and any updates. And, in my downloads folder, I do have some "large" folders containing some TV series. But, the total space taken up on each SSD for all that (ie, the OS and all those applications and "stuff") is a little over 100 gig, ie, less than half. It is a good idea to leave at least 20% of your SDD space free.
So, as you can see, it depends on how many applications and "date" files you want on the SSD.
2. For the applications you want to migrate, you will need to insure that you have the most recent versions for compatibility with El Capitan. Assuming you have Office 2011, version 14.5.8 came out in September, near the release of El Capitan. That is the "earliest" version that is compatible with El Capitan.. Since then, two more versions have been released, the most recent one being V14.6.1.. You can get that from here:
https://www.microsoft.com/en-us/download/details.aspx?id=51174
You will need to check on the other apps you have for such compatibility. I had to upgrade 5 critical apps before I could upgrade from Yosemite, OS 10.9.5, to El Capitan, OS 10.11.1.
3. You will need to connect the two Macs together via a Firewire 800 cable, boot your newer MacBook Pro, and then boot your older one in Target Disk Mode, by holding down the "T"key on the keyboard attached to that older MacPro. Once that is done, the 2 TB hard drive for the old MacPro will appear on the desktop of the newer MacPro as another disk drive. You'll then be able to "migrate"/copy non-OD "stuff" from that 2 TB drive to the "Place" where you want it on your newer MacPro (the 128 gig SSD, or the 2 TB HDD).