One word:  shotgun.

Rob, the lesser of two evils is joint registration like you said. If it is okay for your wife to have access to your firearms, joint registration shouldn't be a problem. 

The answer may be buried in the statues somewhere, but clearly asked:  If my wife were to use one of the guns registered to me inside out house for defense, is that a major problem?  Suppose if I am home, not an issue at all, but if I were away?

I know, the easy thing would be to get them all registered to both of us, which she is amenable to.  Luckily she has her NRA cert and is not averse to being fingerprinted and all.

There is a section in the HRS that allows firearms to be loaned to others for a short period of time as long as they are not prohibited from possessing them.

As long as it was determined to be justifiable self defense, who the gun is registered to doesn't matter. 

Without a painstaking reread with a proctologist's eyepiece on, I thought that loan period was only for long guns, pistols strictly prohibited from even momentary loan.

I have covered this in class in multiple situations.   There is a hawaii case with a person using a handgun in the home for offensive purposes but it was registered to another person in that home. The individual was ultimately charged with possession of an unregistered firearm.   One could argue that it was a criminal act blah blah - but the fact is they basically found that he "possessed" the gun and it didn't belong to him. 

If someone in your house uses a gun that is not registered to them - they can very likely (and easily) face criminal charges.  Register your guns to all parties involved.  lf I had children, I would attempt to tri-register (although the police won't allow it), but you can't challenge something that you haven't tried to get done later on.  The likely hood of this happening would be small, especially if a female victim successfully defended her domain against an attacker.  The political and media fallout from charging that individual would be bad.  They would also have a pretty damn easy choice of evils defense in the case; I couldn't see a jury convicting anyone of that (under otherwise lawful circumstances).

she should get her own handgun.
problem solved. 

You see the irony in this proposed work-around?  The same anti-gun law that restricts use of a handgun to registered owners would result in MORE guns in homes.

I love when the results of stupid laws are 180 degrees from the intended effect!!

I assume that specifically applies to handguns, as long guns can be "loaned"?

she should get her own handgun.
problem solved. 

I get what you are saying, and I would say yes.  But, it might be hard to say that if you were deployed 2-3 months ago (you can only loan for a short period of time).