This type of logic is hilarious. Grayson could've called the many omegas he has on speed dial to help his brother. But he decided his best choice is to try to make him have relations with an animal because what? He couldn’t be bothered to pick up a phone. It’s like throwing somebody a rotting plate of google because they’re hungry instead of walking two feet and giving them a plate of actual food. Justifying a characters shitty actions because you like a character is insane. Anyways Greyson is going to get cheated on and treated like shit I’m happy
As I said, for him it was Chase was going crazy or die. I don't think he would have tried that if he had another option. The option of an injection most likely came with his dad.
But that is all hypothetical, the characters are that messed up because the author wants them to be, so it's also up to the author why they are like this. None of her dominant alphas is normal.
And don't forget you are reading omegaverse.

You literally have a pet dog of your own, cmon..