Being a DAYLIGHT studio, you understand you can only shoot while there is sufficient sunlight outside. Bummer. But at least daylight's free!
You need to control the light coming in. With a daylight studio, you don't necessarily want light streaming in DIRECTLY through a window. Unless it is a big window which can be blanked off with white muslin sheets or tracing paper to soften the light,. So how about letting the light come in through the roof, then bouncing it all over the place to get that nice, white, cotton-wool effect? Imagine mommy and daddy dressed in white, their baby wrapped in white cotton, in their arms, the background pure white, the light soft all around ... That's the look that you want lifestyle family portraits.
So how do we do it? We deck out the inside of the studio in white. If you can't or won't paint the walls white, get big polystyrene (Foamalite) boards from firms such as Sagex, have them cut to 2x2m, and put them to the left, right and back of your room to act as white reflector walls. The bigger the better. Their slightly mottled surfaces spread the light around softly, giving a really pleasing effect. You can paint the floor white, but if you can't, buy a large sheet of white hardboard (Masonite with white side), and deck the floor with it to reflect light upwards, filling in shadows under your subject's chins and eye sockets. You may also add a polystyrene board set at an angle in front of the subjects to help bounce overhead light back into the subject's face.
Finally, the roof - soon to be your main source of illumination. If you can, get one or two roofsheets in the garage replaced with translucent white IBR sheeting that will allow sunlight to be filtered into the roof - not direct sunlight, but rather diffused, soft and pleasing light. These sheets are the same as corrugated roof plates, but made out of a plasticky material that will soften the light.
If you can't replace roofsheets, you can try emulate the effect of the sun by pointing two strong security lights (those outdoor sealed beams with 150W bulbs) towards a white ceiling. Make sure your lights don't spill directly onto the subjects - place them to be on stands 1 meter or so from the ceiling. Not closer, since they need to spread their beams, and not much further, since they will spill onto the subjects. You only want reflected light, not direct light. If some of the light strays directly onto the subjects, use card board or wood panels to flag them off. Place the two lights on either side of the subjects, facing 45 degrees inwards from the front, and make sure their beams overlap to give a nice, even spread of light on the ceiling. This will give a similar spread of light on the subjects. These lights are hot, so take care you don't melt anything!
You're almost ready to shoot now. Don't shoot on Program mode - with all that white around, your camera lightmeter is bound to be fooled into underexposing the subject! Take a close-up reading of the subject's face, or meter off a neutral grey card placed where the subject will be. You need to expose for the person's skin tone, on Manual, and slightly overexpose your background to knock it out and force attention to the people in the foreground. You may have to increase the ISO on your camera to allow a shutter speed that will freeze any movement. Try shooting at no less than a 60th of a second, and stop down to the appropriate aperture for that speed given the amount of light available. At 400ISO, you could for instance be shooting at f4 at a 60th. Test your system before you bring your subjects in so that you may concentrate on the shooting, not the lighting. Happy shooting!