Hey there, is Hayley spayed? Also, how long ago did you get Bentley and how long has it been since he was neutered?
When trying to bond you want to wait a month after the neuter/spay, because hormones will still linger for up to a month (sometimes a little more) and it makes it hard to bond if one is fixed and the other isn’t. Rarely does it work.
Pre-bonding, which is putting them in each others cages/pens/areas every day or two. So hayler in bentleys area, and bentley in hayleys. after a day or two, switch back. Then another day or two, switch them again, etc.
This gets them used to each others scents, and helps them to become less aggressive towards each other. After about A couple weeks of this, start introducing them to each other in short sessions (about 5-10 minutes) and If there’s any aggression (like the grunting) separate them and do some more pre-bonding.
But since they already kind of know each other, just do a week or two of pre-bonding. Then do 5-10 minute sessions in completely neutral territory. Set out some hay, veggies, treats, etc. To help distract them and it could help associate each other with something good (food).
That’s what I suggest if both have been fixed for more than a month.