What metering mode are you using?
With subjects that close to the background Ron is right, using f/2.5 to f/6 doesn't make a lot of sense if selective focus (a shallow DoF) is why you're using such wide lens apertures.
Keith, even with the family moved away from the background, wouldn't you still have a tough time getting the entire family tack sharp using f/2.5 just because of the number of people and the shallow DOF?
Point of focus (PoF) distance has more of an affect on DoF than lens aperture does.
In that photo, the point of focus distance is such that it looks that the DoF isn't so shallow to be an issue for focus on the people.
Using a Nikon D3000 @f/5.6 and a PoF distance of 12 feet, the total DoF is 4 feet, and at 15 feet the total DoF expands to 6.5 feet.
Using f/2.5, at 15 feet the total DoF is almost 3 feet.
No doubt, 1/20 is to slow a shutter speed for controlling camera shake and the slight movements portrait subjects make. For portraiture I didn't use less than 1/100 for my shutter speed.
But the bigger issue with the image is the over exposure of the subjects.
The D3000 has 3 light metering modes - Evaluative, Center-Weighted, and Spot - page 74 of the D3000 users manual.
I suspect the OP has a lot yet to learn about metering modes, and depth-of-field.
The D3000 has 3 light metering modes - Evaluative, Center-Weighted, and Spot - page 74 of the D3000 users manual.
Understanding Camera Metering and Exposure
Understanding Depth of Field in Photography