[EDIT: This would be applicable if you were using iCloud Photos on the old phone, and the photos on it were already stored in iCloud Photos under your father's Apple ID.]
Apple has a service for transferring a copy of the photos and videos in your iCloud account to Google Photos.
Transfer a copy of your iCloud Photos collection to another service - Apple Support
Transfer a copy of your photos and videos to iCloud Photos – Apple Support
I suppose that if you had a Google [Photos] account, you could
- Transfer photos from your old Apple Account (your Dad's account) to your Google Photos account, then
- Transfer photos from your Google Photos account to your iCloud account
The question is how much resolution, metadata, etc. you might lose in the process.
It's a pity that there seems to be no article describing how to transfer a copy of iCloud Photos from one Apple ID to another (which you would think would be a more direct transfer, and one that wouldn't lose resolution or metadata).