From a professional of over 25 years....
Your 'behaviouralist' is not remotely educated or qualified - dominance is NOT, nor ever will be, the cause of a behaviour problem
Nor will being allowed on the bed.
Peeing in places that smell strongly of you scream an insecure dog living in a high stress situation.
All your descriptions of how you're managing these dogs also screams of a high stress situation and because your actual, factual dog behaviour knowledge is limited at best, you are at risk of making one mistake too far, and soon.
Do not call a trainer. They train dogs.
Do not call anyone who mentions dominance, alpha etc etc.
Certainly do not call Graham bloody Hall, chances of him dealing with an XL bully are low anyway but if he did he'd want around a grand off you and is incapable of solving the problem.
https://www.ccab.uk/practising-ccabs Check out here. This is who you need.
Don't expect to call and instantly get help though, you'll need to give them a full and detailed history and set up an appointment. You would both be expected to be there, whether its remote or in your home.