The Marlin Camp 45 isn't a "battle rifle," but for home/property defense distances, it's more than capable of doing the job. Any family member capable of holding it steady could probably handle shooting it. It won't add much to MV of the .45 ACP round, but its longer sight radius and the steadier platform give it a much longer range than a handgun in the hands of most people. It will probably be more enjoyable for more family members than a lot of other defensive long guns, and getting non-enthusiasts to put in practice time can be a challenge.
As others mentioned, the blast from shooting it indoors -- especially w/o ear protection -- is a lot less than that of a shotgun or a .223 carbine. It should also produce less muzzle flash than a shotgun or .223. A PCC is also allowed at many indoor ranges where rifle-caliber firearms are not permitted. Even at an outdoor range, though, the lower flash and blast may make it friendlier for beginning shooters.
I'm not bothered by the "small" capacity. A 7-, 8-, or 10-round magazine is probably plenty for 99.9% of home/property defense situations, and it's a heckuva lot quicker to reload than any long gun with a tubular mag, like a levergun or a pump.
In the event of a disaster like Katrina or Sandy, or unrest like the '92 Los Angeles riots, I would feel pretty comfortable keeping my family safe with a Marlin .45 ACP carbine.
I'd buy it in a heartbeat.
Keep safe,
Dirty Bob