Why get a dog of a revolver?
Please excuse my going astray from the letter of the question. I am trying to address the need expressed rather than the literal question.
(note: I do get around to answering the literal question eventually)
Why get a dog of a revolver when they (your girlfriend's Dad's family) can be better served by an actual dog.
Self-contained. Not only a defensive weapon against intruders, but includes intruder-detection software and hardware already built-in.
A dog provides exercise (if you train with your dog as much as you should train with a gun).
A dog provides psychological counseling and never betrays a confidence.
You can warm your feet on a cold night against a dog's back (try THAT with cold steel.)
MOST IMPORTANT: Use of lethal weaponry requires (responsibly) recognition of the legal and psychological implications and risks. The emotional and legal aftermath of pulling a trigger on another human being requires a lot of preparation, training, knowledge and realistic expectations. You can prove yourself (to your girlfriend's father) an upstanding and proper steward of his daughter's well-being if you discuss these matters with him. He has shown a trust in you by asking for this advice. I suggest your return the favor by giving him the WHOLE picture. Not just on the firearms available, but on the other stuff needed, like cleaning, training, practice ammo and an increase in homeowner's liability insurance. He will respect you all the more for it.
Also suggest creating a defense plan to react to a home invasion as well as smoke or fire in the house. Pre-planned changes to the home perimeter is a good idea as well. Exterior lighting, proper arrangement of bushes and lawn ornaments, etc help steer potential threats away from your home in favor of easier targets. All to be considered in addition to (and possibly before) firearm choice.
Also note that the second part of the question involved ease of use for his wife and daughter to shoot. Handguns (auto or revolver) require a LOT of practice to master and to shoot well. Long arms are MUCH easier to hit with. A brand-new pump shotgun can be had for around $300 (Mossberg, and Remington 870 is on sale in Anchorage next week for $325 for Bass Pro's opening a new store here) While 12 Gauge may be a bit heavy for the wife and daughter, they are not unmanageable and light loads are available. 20 Gauge (or 16 Gauge) are more manageable for some with less upper body strength.
My house gun is a 6" .357 Magnum Security Six loaded with .38 Special frangible ammunition (that is designed not to penetrate my exterior walls) near by bed and 12 Gauge pump in the bedroom closet.
I can choose from among: 4" Sec.Six, 6" Dan Wesson .357, 5" 45 ACP 1911, 45 ACP Taurus Millenium, 5.5" an 7.5" 44 Magnum (in which my ammo choice would be 44 Specials) and 7.5" 454 Casul (in which my ammo choice would be 45 Colt). Not to mention Taurus 9mm Semi-auto. I also have 4" and 6" Ruger GP100s, but eschew them because my Sec Six is lighter and handier.
I chose the 357 because it is light and handy and I am accurate with it. I keep thinking about using the larger, slower 45 ACP and 45 Colt, though.
A police surplus Smith & Wesson Model 10 or Model 15 (38 Special) might just be the ticket, though I much prefer the Ruger double action revolvers for a number of reasons. But the Smiths are good and proven guns. 39 Special ammo is available and shootable for the whole family and has a proven track record for social work. Despite some highly hyped failures, they are rare; most bad guys will stop when the first hole appears in their flesh or upon the appearance of an armed defender with determination and confidence (remember the training and mental preparation) on their face(s).
Thanks for asking our advice, and again, please forgive my detour to the canine, non-gun, relationship and long gun suggestions.
Lost Sheep
edit: Please don't take my lack of mention of Armscor, Taurus or other revolvers as denigrating them. I have a Taurus 22 revolver which works great and I would expect nothing different from their other models. I know almost nothing about Armscor. Don't forget Charer Arms, either.