Thought I posted the code to merge two albums but it appears I did not. So here it is:
import photos
from datetime import datetime
albums = photos.get_albums()
# prob better ways to do this but this works, loop through albums and create list
# where album name equals name in quotes, then take first one (should only be 1)
sourcealbum = [a for a in albums if a.title == 'put album name here'][0]
print(f'Nbr photos in sourcealbum: {len(sourcealbum.assets)}')
sourcealbum_2 = [a for a in albums if a.title == 'put second album name here'][0]
print(f'Nbr photos in sourcealbum_2: {len(sourcealbum_2.assets)}')
# this requires that the dest album exists as it will not create it
destalbum = [a for a in albums if a.title == 'put dest album name here']
if len(destalbum) > 0:
destalbum = destalbum[0]
print(f'destalbum: {destalbum}')
# first create a merged list of both albums
mergedlist = sourcealbum.assets.copy() + sourcealbum_2.assets.copy()
print(f'Nbr photos in mergedlist: {len(mergedlist):,}')
# sort merged list by creation date
mergedlistsorted = sorted(mergedlist, key=lambda x: x.creation_date)
# add the sorted assets to the destination album
destalbum.add_assets(mergedlistsorted)
# I always put this at the end in scripts to know for sure when it finished
print('***** DONE *****')
So this merged to albums with about 900 pics in one and 800 in another almost instantly. The resulting album had 1700+ pics in the correct order and the pics were not physically duplicated. Do not know how I could have done this any other way on the phone. I do not sync my iphone with a Mac so if I did this on Windows I would lose the live photo part of the iphone pics.
Thanks everyone that helped!