So, when you get a visitor, i take it, your dogs go crazy, leaping about, and if the dogs had the chance, they would even bite the visitors?
YOU MIGHT HAVE TO START FIRST, with distance work, outdoors,
with one dog at a time,
staying at whatever distance your dog needs to be calm, rewarding calm behavior, and leaving the unknown person. That's it,
no contact is involved, no real close proximity is involved, and it might be 50 feet away for your dog to be calm. You are just working to help the dogs, one at a time, reduce their aggressive reactions to unknown ppl, and gets rewards for calm behavior at the sight of unknown humans.
while ongoing desensitizing work is in progress, if you get a visitor,
One thing you could try, is having dogs not by the doorway.
Doorways can be triggers for many dogs.
Have dogs in shut door room, while you let in visitor. You might need Isis and Jinx is different rooms than each other, to reduce re-directed aggression onto each other as visitors arrive.
(later on, after progress has been made, you can work on dogs being cool near a door opening to a visitor, but,
for now, just keep it simple, and
skip the whole doorway scene for now) We can get to that one later.
While dogs are in other room let in visitor, and have visitor seated, in chair, side of visitor facing the door where dog will come from, and far from that door, too, across the room. Tell visitor to not look at dog, ignore dog completely. I'm sure you know, Cwolf, no forcing contact onto a dog, it works against your progress.
This visit won't be that be much "fun" for the visitor, so you will need volunteers who WILL follow your instructions.

You will have to buy them a dinner for all their help!
For working with
Isis, have no dogs, or only dogs Isis likes, in the room.
Bring in one dog,
start with Isis, she will be easier at this human thing, as i suspect Isis is dog-aggressive, not shy. Go into room with Isis, close door behind you, and give her calming signals. A slow blink, a yawn,...........a deep slow sigh.
Get Isis as calm as you can to bring Isis in...take your time, is no hurry. Your visitor knows the deal.
Bring in Isis, from across room, keep Isis on leash, and if Isis growls,
you can do "The Bathroom Trick" which is detailed in
post #6
in this thread:
http://www.dogtrickacademy.com/members/forums/threads/7-things-that-helped-my-dog-aggressive-dog.4413/
"The Bathroom Trick" is done calmly, and silently. It works great on my aggressive dog.
if you dog is NOT the kind to lunge towards humans who are NOT touching them, it is fine to drop the leash, cuz you will
not be allowing anyone to touch them. You may need muzzles for first exercises, that is your decision, based on however aggressive your dogs are.
Once Isis ever
can be room, and
not reacting, which, really
, if Jinx is not in room, you might be pleased to find is not extremely difficult to get
Isis to settle in a room with unknown humans. Don't push it, don't egg Isis over to anyone, your goal is just calmness, not contact.
It might take any number of these lessons, to successfully get Isis to be calm with a stranger in her house. It might not be something you can get done all at once, even with Isis, who i am hoping is going to be the easier of your two dogs to learn to be calm by strangers.
but once you can bring in Isis, and no reactions occur,
You have many options now. Reward non reactions.
Calmly praise the dog, and give yummy treats for nonreactions.
You can ask Isis to go to her mat.
OR
You can have visitor do a big yawn,
and then glance, not stare, but calmly glance at Isis with soft eyes, offer a slow blink, glance back away, and toss a treat for Isis in a gentle smooth motion, not an aggressive fast toss.
Later, visitor can do a deep sigh, and toss another treat towards Isis.
I'd keep these first lessons short, and have them occur frequently, like every other day. Make these fun for Isis,
not exciting, she is excited enough already, but
fun and pleasant.
I really think, you will meet great success with getting Isis cool around humans.
Then, you'd have to work with Jinx, also separately, and i'd strive towards having Jinx go to
her mat, in another room, as
her final goal, but Isis may be calm across the room from visitor. Since both dogs have bitten ppl, i would not want either dog close to an unknown visitor, if the visitor suddenly spoke loudly or animatedly or gestured, and dog is close, it could be too much for a dog close by, you probably should strive towards "go to your mat" as goal.
I think having BOTH dogs in room together greeting a visitor, i'd think i'd wait on that exercise til you are very confident that each dog was solidly okay and calm by their self, before even trying two at once, and i'd think, you'd need help, as well. That is for further on down the road.
There are many many other approaches, to getting dogs to stop reacting inside a home, but, that one is worth a shot.
ALSO, are these boxer dogs getting at least two good long walks a day???
or some running time daily?? Earlier i had thought it was your mastiffs who were aggressive, but, it is your boxers, right?
Exercise does not cure aggression, but lack of it can add to the whole mess, if the dogs are boiling over with unspent energy. Boxers are higher energy dogs, and the dog breed info thing says that they might not be great to leave alone around prey..