In a large bowl, mix ground beef, sausage, onion, garlic, bread crumbs, Parmesan, parsley, and eggs gently with your hands until completely incorporated. Season with salt and pepper and form into 24 balls.
Set Instant Pot to Sauté and heat oil. When oil is shimmering, add onion and cook, stirring occasionally, until onion is soft, about 5 minutes.
Stir in tomato paste, garlic, and oregano, and cook until fragrant, about 1 minute.
Add crushed tomatoes and season with salt and pepper, then add meatballs.
Secure lid and set Instant Pot to Pressure Cook on High for 8 minutes. Follow manufacturer’s guide for quick release, making sure to wait until the cycle is complete before unlocking and removing the lid.