A bit late now for Thxgiving.. but good info for anytime of the year so here we go..

You need to practice and practice and then review your settings.. if you are using a DSLR, then you should always shoot in RAW mode which allows a ton more latitude in post processing than jpg... that should always be your first thought.

Then, you will have an issue with the number of people in the shot.. if you set the aperture low, then you will get in a lot of light.. but your subjects will be subject to blur... depth of field is also controlled by your aperture so a low one with produce less DOF and therefore more chance to blur someone;s face in the group unless they all fall on the same plane.. (which will not happen typically in a group photo).

So, the key here is to set the aperture to something like F8 or F11 to ensure everyone will be sharp. However, this will lower the amount of light reaching the camera and will lower the shutter speed. So, you then need to bump the ISO up a bit. ISO 400 or even 800 for an indoor shot on most DLSR's will give you good results..

The final advice.. external flash.. they are invaluable for indoor photos and will allow you to get the best results when used properly. The onboard flash will just not give you enough power.. so think of getting a speedlight for the camera or an external flash.

Also, keep in mind.. that if you shoot RAW, you can regain at least 1 full stop of light in exposure and can also bring back darker areas in the image via curves... always better to underexpose than overexpose..

Hope this helps... try to avoid Auto mode... you won't be truly using the DSLR if you do - it basically becomes a heavy P&S.