migrate triple-booting legacy-BIOS Linux-w7-w10 to EFI board

Recovering data from my sudeenly departed son's computer was a job and a 
half, but it's mostly done. He had a huge server tower and I think he 
was amusing himself with RAID (which he didn't need) and encryption 
(which he didn't need) and so on!

Drives:

#1
500gb ssd with strange partitions for Linux and I think some created for 
future Linux OSes, could't figure out his /home partition setup, 
possibly raid.

#2
1tb ssd hosting fat and ext4 data PLUS a w7 and a w10 partition

#3
4tb data


#4,5,6 in a Linux-Raid array, all data

I copied out the #4 data set, cleared those drives, and released the 
tower to the executors for liquidation. Then I also backed up what ever 
other data I could find to other drives on hand.

Plugged the # 1,2,3 drives into my own very similar computer; couldn't 
believe it when everything just booted right up, even the two window 
installs!  This gave me the idea that I can relax and take my time doing 
the rest of the recovey, filtering and disposal as time permits because 
I can now just boot my son's systems on my own compouter. But it's my 
OLD computer.

_____And now shit hit the fan

I'm moving to a new and inevitably UEFI box, just plugging those 3 
drives in doesn't work any more, so...

I copied the #1 drive to a 1tb ssd to have more space, then did a fresh 
Linux (Tumbleweed) install to get EFI bootabilty. With that new #1 drive 
and his other drives including the #2 with windows on it also plugged-in 
I ran Yast to set up the EFI boot. I can now boot either my temporary 
facilitating Linux install OR my son's Linux (Leap-15.4) on the new 
EFI-BIOS board.

But I cannot boot his windows, for that I'd have to keep my old 
Legacy-BIOS box which I don't want to do (I can unload it for a few 
hundered bills).

Not knowing windows much I think I could do a w7 and a w10 fresh install 
after having done two 'windows backups' on the legacy box and then try a 
recovery from those windows-backup files on the new w7 and w10 installs 
on the EFI box. There's GOTTA be a simpler way   ..I hope.