Need your digicam advice

I have a Panasonic Lumix LX30, it takes very nice photos in sunlight outdoors but indoors the quality is variable. Some photos are quite nice but some are grainy for no reason that I can understand. Especially photos taken in my living room, these never turn out satisfactorily. I suspect this is something to do with my camera setting, ISO sensitivity, Whiteness, anti-blur etc., but so far I have not been able to solve this problem.

Please have a look at my sample photos below and advise. Thank you.

(Please click on the images below for full size, the graininess is highly visible on the full size images)