Help Family Christmas Photos I Don't want to mess this up

Hello, I have been elected as the photographer for this years family Christmas Eve indoor party.  I am only a beginner with a dslr ,  but since I have the best camera in the family,  they want me to take all of this years photos.  I would really appreciate all your help.

I have a Canon T3i with a EF 50mm 1.8 and a EFS 18-135mm 3.5-5.6 IS, both Canon lenses.

I have taken indoor party photos with the 18-135mm lens and camera set on auto before but the photos are not the greatest.  They look good on the camera but not so good on the computer.

These are going to be very important photos  since it may be the last Christmas that some of the family members will be around, some are elderly.

I would also like to take some videos.

If you could suggest settings I should use for both photos and some videos, I would greatly appreciate your help.

Thanks

Marina