I think my younger male dog is resource guarding me from my older male dog

We have a one year old border collie and I've recently noticed inappropriate behavior toward my seven year old male mix breed. The border collie will growl or snap at my older boy if he approaches me or if I'm giving him attention. If I call my older boy, he gives him a kind of hard stare so my older boy won't approach me and will turn around and go the other way. They used to be just fine with being in the same space as me and even used to lay together on the couch sometimes. The BC would lay in my older dogs crate with him and sleep/play with toys together. They literally slept next to each other on the bed with us and our BC was laying with his head on our older dog. With this recent behavior our older dog is mostly isolating in his crate (he's older and likes to sleep in there most of the time anyway, but he's staying in there now during times when he'd usually come hang out with us, like after dinner). He will come out and hang out with us if the BC is crated, and last night he laid next to the couch we were on while the BC and beagle were in the couch.

This behavior does not apply to my five year old beagle, I can pet both of them at the same time and interact with her as normal with no interference. He still cuddles with her and plays with her as normal. He does sometimes get jealous when my husband is petting her but not as severe as what we are seeing with our other male dog.

Is this gender related? Is it something to do with dominance? Our BC just turned a year but both he and our older dog are neutered. Our older dog does not engage in any aggression with our BC even though he is bigger and could objectively put the younger boy in his place if he wanted to.

From what I've read online, I understand that it's bad to either try to reassure my BC (as this could reinforce the guarding behavior) or to punish him for it. I am having a hard time finding anything on this specific type of situation since it seems to be primarily directed at my older dog, not all dogs at large. To be clear, I do intend to consult on this with a coworker who is a certified dog trainer, but I won't be able to for a few days and I am hoping to gather more information in the immediate to make sure I am handling this situation thoughtfully and appropriately. I really appreciate any constructive thoughts or information anyone is able to share with me.