you've started off right, by talking about it between your brother and all the spouses.
next step is to start getting some info on potential financial support or insurance. yep you already said that you don't have much discretionary funding at the moment, but at least get an idea of the types of insurance available, and cost ranges; the earlier you start them, the cheaper they are. those same people can give you some basic info on preparing for possible nursing home or assisted living situations. There is a good deal of gov't assistance available, but you have to have your ducks in row quite a bit in advance. The old rules allowed the government to "look back" 2 years for your parent's financial situation, but that rule is changing. If you want to preserve anything of theirs, start laying the groundwork now.
Also discuss the situation of having your parents move in, or move close. this is a touchy area and expect alot of fireworks, but bring it up and get it into the open. there are many variables that can work. we are looking at the same situation for the 4 parents (mine and my wife's). An interesting option may develop in a house that's for sale right next to ours; we are considering buying it and renting it out, keeping the option open that eventually it will be used for our parents. that way they will be close and we can help out, but everyone will still have their own space.
on a related note, break out the video camera and start taking it with you everytime you visit. just set it up and let it record, while you talk at the table, eat, play cards, have b-days. after awhile they forget it's going and you will be able to record memories.