As you can see in the error message (and you also mentioned it), the problem is that the folder contains multiple versions for the pseudos for a given element. Moreover, it contains scalar-relativistic as well as fully-relativistic pseudos. Probably, you don’t want to mix them, so grouping them in different folders (and also in different pseudo families in AiiDA) might be a good idea in general.
I remember encountering something similar when I tried to install these pseudos. The following code will move the pseudos into different directories, based on the version and the type (i.e. SR or FR). It expects that the subfolders SR_1.0, FR_1.0, SR_1.1 etc. already exist in the new directory new_sg15. You would need to adapt the directories accordingly to your demands.
import os
import shutil
import re
for filename in os.listdir('./sg15'):
# Extract element and version from filename
el = filename.split('_')[0]
version_match = re.search(r'-(\d+\.\d+).upf', filename)
version = version_match.group(1)
# Check if scalar relativistic or fully relativistic
sr_fr = 'FR' if 'FR' in filename else 'SR'
# Copies to the directories FR_1.0, SR_1.0, FR_1.1, etc.
source_path = os.path.join('./sg15', filename)
destination_path = os.path.join('./new_sg15', f'{sr_fr}_{version}', filename)
shutil.copy2(source_path, destination_path)
Afterwards, you can install the pseudo families using the new subfolders, e.g. the fully-relativistic ones from version 1.0:
aiida-pseudo install family -P pseudo.upf new_sg15/FR_1.0 oncv_sg15_FR_v1.0
Since some pseudos are only present for a certain version, you might want to merge them, e.g. version 1.1 and 1.2. In that case, remember that only one pseudo per element should be present in the directory that you are trying to install.
Hope that helps.