Hi there,
I am sorry to hear about the passing of your father. My condolences.
Unless your father added you or someone you know as a Legacy Contact on their Apple ID, it will not be possible to remove the Activation Lock from his Mac. You can check if you were added as one of his Legacy Contacts by doing the following:
On your iPhone, iPad, or iPod touch:
- Go to Settings, then tap your name.
- Tap Password & Security > Legacy Contact.
- If you see your father's name, you're one of his Legacy Contacts. Tap his name to see more options, including viewing the access key or starting an access request.
On your Mac:
- Choose Apple menu > System Settings (or System Preferences), then click your name (or Apple ID).
- Click Password & Security.
- Click Manage next to Legacy Contact settings.
- If you see your father's name, you're one of his Legacy Contacts. Click Details next to his name to see more options, including viewing the access key or starting an access request.
If you don't see an access key, you were not added as a Legacy Contact. You can learn more about Legacy Contacts here: Request access to an Apple account as a Legacy Contact - Apple Support