Everyone who has taken pictures has suffered from his or her pictures being inexplicably yellow. The answer is simple: jaundice. Just kidding. It's that you're afraid. That's not it either.
It is the fact that every light source burns at a specific temperature. The temperature is measured in Kelvin. Lower Kelvin means that the light is burning at a lower temperature.
If you buy a regular, old-fashioned light bulb, it uses tungsten as the filament that burns when you turn the light on. Specifically, tungsten burns at around 3000º Kelvin.
At that temperature, the light it produces is slightly yellow. If it burned hotter, it would be more blue.
So, the answer to the question of 'why are my pictures yellow?' is that you're using a tungsten lamp and it's producing a yellow light. Since your family is being illuminated by those tungsten lamps, your pictures are yellow.
There are two ways to fix this. First, you could change the white-balance on your camera so that it's set to 'tungsten.' If you choose the LIGHTBULB ICON in the white balance settings in your camera, the camera will automatically adjust your camera's sensor to take into account that the light source is a tungsten bulb. The camera will add blue to the image to balance the yellow light.
Or, you can simply change the temperature in Lightroom. With this picture, I just loaded it into Lightroom and adjusted the yellow-blue slider so that there was more blue than yellow. This is what I always do rather than take the time to change the white balance while I'm shooting.
The result is a more accurate color-balance. We don't look so jaundice! Yay for healthy skin-tone!
I hope this helps you understand why your images are often yellow and what you can do to fix them.