Is it normal for retirees to be negative?

Negative attitudes are common.  Many elders feel social stress in the dining room of retirement communities.  Complaining about other people is often a defense mechanism. 

One way is to encourage them to reach out to people they like outside the dining room.  Then it is nice to make a date to have dinner together.  This could be with another couple or with one or two single friends.  Your parents are used to being together.  It is easier to cook than to reach out and make friends with other people. 

Another way is to often go to meals with your parents. Create a convivial sense of genuine curiosity or interest about other people at the table. Sometimes older people are looking down.  They seem to be focusing on their food.  When asked a question, the person looks up with relief.  Often, you will have to ask questions several times. The key is to make the conversation ordinary and keep in in the present moment.  "Do you like the rosemary on this chicken?"  Have you ever seen the chef?  I've heard that he wears a white hat.  I love these flowers!  Do you know what they are?  What is your favorite flower?  This chocolate pie is good.  Do you make pie crust?  I buy mine frozen.

Simple questions can grow into more general and interesting discussions on happenings in the news. When I eat lunch with elders, I try to read the headlines in the paper and scan the metro section, looking for something interesting or funny or even weird. 

Good conversation will soon drive away the undesirables; there is even a chance that some of them will transform into more interesting people.  And you parents will eventually begin to shine as leaders of the dining society. 

This is a great answer. There are new social skills that begin when a person moves into new social situations. Think college freshman or even assigned seating on a cruise ship. There are always negative people around it takes awhile to figure out who you want to spend time with.

I usually try to have a topic ready e.g a TV program from the previous evenings offerings before going to dinner which often helps to generate interest in subjects different from the usual health issues or the quality of the food with which we tend to become preoccupied. It leads to my telling about the program if no one else watched it, and their desire to see next week's episode, or to share opinions about the shared experience. Everyone enjoys reminiscing. Turning discussion on to what we used to enjoy doing such as dancing, cycling or managing during the war years, for instance, will usually stimulate contributions from the other five at our table.

One of the things that struck me about this question the most was how it seems to me that maybe you are more concerned w/ them not eating w/ others moreso than they are. I personally have seen folks who are better off physically not want to bother or be wrangled w/ the folks who are more dependent on others for help. If a less stress free eating environment is what they want , then I say don't make a big deal about them wanting to eat in their apartment by themselves-at least they do have each other to share time with:) A lot of folks, as I'm sure you are aware of, don't have anyone to eat with in dining room, let alone in their own apartment, so I wouldn't make too much out of it at all!

I say this from the perspective of an Ombudsman who works in a mostly Medicaid funded nursing home, where private rooms are not available and most of the folks are 'lucky' they can make it to the dining hall and eat with others; I do get complaints from residents who say they would reather eat in their room then have to deal w/ all the folks who aren't like them in dining room. Some residents ask for food, need help eating, or are hard to understand audibly, so these folks feel awkward about sitting at table w/ them day after day, and I completely understand where they are coming from- Besides, there are other opportunities for residents to socialize w/ others , other than at mealtime:)