I have had friends stay at The Montri Hotel, and they haven't had any problems with "joiners".
Seven Suns Guesthouse will probably have a Christmas lunch, with possibly quite a few gay guests -
http://www.sevensuns.net/
The Sheraton Hotel usually has a good buffet dinner Christmas Night - I don't know about a lunch - phone 053275300.
The Novotel Hotel also has a good Christmas buffet - 053 225500-4,225505. as does the Amari Rincome Hotel. The La Gritta Italian Restaurant, in the Amari has an excellent Christmas dinner -
http://www.amari.com/rincome.