This is a classic case of fighting for pack hierarchy. Yes, this can be resolved but it might not be fixed. The solution greatly hinges on you and your bf's alpha ranking and Hank and Lola's temperament.
In my pack, my husband is a natural at being the strong leader that none of the dogs want to challenge. I'm not. I'm a wimp with the dogs. But I'm the primary caregiver. I have 3 dogs - Gizmo, a 15lb male bichon, is the first dog and thinks he's the alpha but his small size makes him ineffective as a pack leader. Bully a 6 year old 65lb female bulldog is an alpha-type female. She is stubborn as all get and I have a difficult time getting her to do something she does not want to do. But I control her food so tolerates my commands. She used to try my husband but she's learned her place. She growls at Gizmo if she gets bothered by him but Gizmo would just run under the couch to escape so nothing much happens. Angus, a 2 year old 50lb male bulldog is the latest addition to the pack. He's an omega dog so Bully bosses him around. Angus tries to dominate Bully and Bully would growl and get her jaws on Angus neck and Angus would immediately flop down on the ground in surrender. We keep an eye on them and so far we can just let them fight it out. Sometimes if the growling gets too much, my husband calls both their names sharply and that's enough to get them back on their good behavior. They don't play with each other on their own. Bully only plays if the humans are playing too. Angus and Gizmo, on the other hand, are best friends. Gizmo bosses Angus around and Angus thinks it's time to play. So, in our pack, everybody has their place and they stay within its bounds with only a few harmless, albeit loud, skirmishes.
Why this works: All the dogs recognizes human authority because my husband consistently does not tolerate misbehavior even when it's cute. Bully is 4 times bigger than Gizmo - the only dog that refuses to give up his ranking to her. Angus is naturally an omega dog, scared of his own shadow.
In your case, for a few weeks everything is hunky-dory because Lola is new to the place and is still trying to get acclimated. Hank is fine too because Lola is falling in line. Now, Lola gets comfortable and naturally establishes her dominance in the pack. Hank is a puppy in her eyes and so she pushes to dominate. Hank, who has been in the pack longer, resists and tries to put her back in line. It's not working because both are wanna-be-alpha-types so they end up fighting to draw blood... this could easily turn into a fight to death. I don't think the hip dysphasia had anything to do with this. It's just a coincidence.
How this can work: You establish your alpha ranking and put both dogs firmly in omega. That means, you'll have to pay close attention to your dogs at all times. If you're occupied and can't do this out of the corner of your eye, then they both get to stay in their kennels. You can tell when one starts to challenge the other because he will come stiff from head to tail, head down, eyes staring. Every time you see this, snap him right out of it and "put him in the corner". The object is to make both realize, you're firmly the boss of them because then, it will lessen their desire to dominate. Other ways to establish this is for you to control their food. They eat on your say so. There are other ways which can be google'd. Try googling "resource guarding", this would be the same concept.
If this does not work (both dogs remain aggressive in addition to alpha-wanna-be's), then you will have to keep them separate at all times, which may be accomplished by assigning a dog to their own part of the house.
Hope this helps. From experience, my husband successfully raised 2 un-neutered male alpha-type dobermans. Yes, he incurred $800 worth of stitches after both dogs ripped each other's throats out before my husband got them in line but that was their last bad fight ever and both dogs lived to be 12+ years old. My friend, however, could not get her boxer to get along with her other dog (she's a professional dog trainer) so the boxer lived in an outside dog condo.