iPhoto Libraries from old OS

Dear Apple Community,

I am experiencing issues with my iPhoto and libraries that I have accumulated over the years from using different Mac OS's and also the transition from Apple processors to Intel processors(perhaps a common issue for Mac users).

My issue is this:

1) I have 2 iPhoto libraries - one is 35.56GB and is stored in my iCloud drive (although it has a strike through over the cloud image) and the second is on my Mac's (Airbook 2019 and iMac 2017) and is 88.58GB in size.

2) Over the years I have always kept these libraries on external hard drives as back, during which time Apple transitioned to Intel processors and new OS - therefore compatability became an issue due to the upgrading of the iPhoto app, cloud storage etc.

3) I am now unable to access both libraries and only have access to the 2nd larger iPhoto library.

4) If I try to import the smaller iPhoto library nothing happens and I still only see the larger photo library.

My concern is obviously being able to access the smaller library as I am unable to access the photos within.

Could you please:

1) Suggest any processes/techniques that I can do myself eg. reinstall old OS on one of my Mac's to access the other library

2) Offer advice as to 3rd party software companies who specialise in supporting iPhoto library issues ( i appreciate you may not be able to do this)

Many thanks in advance for any help offered.