How to organize photos from different locations into one

Joshua,

If you can afford to pay temporarily for additional cloud storage, I would try to merge your libraries in iCloud Photo Library. It is the only way to merge Photos libraries in a lossless way (meaning - it will keep edited versions original image files paired and preserve the albums and folders). During the upload to iCloud photos will solve conflicts between duplicates across your libraries. Once you merged the libraries in iCloud you can wait for the merged library to sync back and stop using iCloud, if you do not want to use it further.

I discussed the options for merging libraries here: Notes on Merging Photos Libraries

As to removing duplicates - you have to very careful what you are using. Some applications are dangerous and may damage your library beyond repair, see: Using third-party apps to remove duplicate photos might damage your Photos for macOS library - Apple Support

I can recommend PowerPhotos and Photo sweeper. I am using both a lot without problems.

I would not use any duplicate remover or cleaner, that will directly remove the photos from the Photos library. Only applications that collect the duplicates in an album are save to use. You can then delete the duplicates safely by deleting them in Photos from the album and moving them to recently Deleted.

Welcome to the Apple Support Communities!

I understand you would like to gather all of the pictures that you have from different devices and photo libraries into one place. I will do my best to provide you with a basic workflow, but the advice below is dependent on a some information that I need from you:

• What operating system are you using on your MacBook Pro? (Apple menu > About This Mac)
• What is the capacity of your MacBook Pro internal hard drive, and how much space is available?
• Are you currently backing up your computer to an external drive using the Time Machine application?
• How big are your current Photos and iPhoto libraries? (right-click on the library and choose "Get Info" for file size, then open the library to the All Photos album to find number of photos and videos it contains).
• Do you currently have iCloud Photo Library enabled in the Photos app?

Without knowing any of these details yet, the way I would approach this generally is to:
1) Get a new external drive that is at least three times the size of your MacBook hard drive, formatted for Mac OS Extended (Journaled).
2) Make a list of each library and folder and determine the number of photos and videos it contains and what its file size is.
3) Assuming that the Photos library is your most recent library (and most updated software), I would first drag the Photos library to the new external drive (it will make a copy of it).
4) Rename the Photos library on the external drive to "Joshua's Master Photo Library"
5) Open the new master Photos library on the external drive and get an idea of what is inside it. The All Photos album will list all of your images in chronological order with the most recent image at the bottom of the screen.
6) Assuming these are your most recent photographs, if you have not taken the time to organize them into albums, that would be my next step. (ie. Family, Friends, albums for significant events like vacations, weddings, etc.). The albums will help you get a clearer understanding of what is in your main library.
7) The next step would be to open your iPhoto library on your MacBook Pro and compare the images and videos you see in the iPhoto library to what you have in your Photos library on the external drive. I would do this one event at a time, and if the event appeared to be missing from the Photos library, then export the images in the event from the iPhoto library to a folder, and drag that folder to the Photos library on the external drive to import it there. Repeat the process for the photos that you have in individual folders.
8) Finally, attach your iPhones, one at a time, to your computer and review the images that are on them. You can select the images that appear to be new, and only import them into your Photos library.
* Important: If you do not have iCloud Photo Library enabled, then you can delete the images after you have imported them. If you DO have iCloud Photo Library enabled, DO NOT DELETE the images on the iPhone, as they will be deleted from your Photos library as well!
This will be a tedious, time consuming process, but if you do it methodically, and create albums in the Photos library that will help you keep things organized, you will eventually have one master library to work with. (You'll have a nice walk down memory lane in the process.)
You may need to keep Joshua's Master Photo Library on your external drive if you don't have enough space on your internal drive on your MacBook Pro.
Once you have everything organized, I would move all of the old libraries and photos to the other backup drive that you use with Time Machine so that you can access them if needed. Once you confirm the files have copied successfully, you can remove them from your MacBook Pro.
From this point on, you can work with one library in the Photos app. Depending on the size of that library, you can choose whether or not you want to enable iCloud Photo Library to keep all of your photos synced across devices, or create a new System Library and start fresh with the new photos you take on your current iPhone going forward.
Joshua, I hope this information gives you a general idea of how to get all of your photographs and memories organized. Please reply to this thread with the answers to the questions posed above if you need additional help with this project.
Here are some resources for you:
How to use Time Machine to back up or restore your Mac
Format external drives to Mac OS Extended before using with Aperture​ (You aren't using Aperture, but the information about formatting the external drive for your Photos library is the same).
Get to know the Finder on your Mac​
macOS High Sierra User Guide - Photos
iCloud Photo Library​
Enjoy your day!

After you turn on iCloud Photo Library, the Camera Roll album is replaced with an All Photos album. The All Photos album gives you the same compact scroll view, now with all your photos and videos organized by the date you add them.
iCloud Photo Library uploads photos and videos from your Mac System Library. Photos and videos that you keep outside of your System Library won't upload or update across your devices.

You can see if a photo or video has uploaded to iCloud when you open the Photos app and view your library in Moments. Your upload status is at the bottom of the menu. You can also find photos and videos from your Photos Library that haven't been uploaded to iCloud in a smart album on your Mac.

When you delete a photo or video from your Photos app, it also deletes from your iCloud Photo Library and iCloud storage. You can recover your photos and videos from the Recently Deleted album for 30 days.

Good luck with your project, Joshua!