Camlace, either you're increadably sensitive or you've not read the posts in the spirit in which they were intended.
If you've invited your sister then she's done nothing wrong ( although you may be better advised to think and inquire before offering invitations in future). Your comment of " Now my sister has decided to join us so we have a party of 5." led me to believe it was your sister's idea not yours or that she had perhaps changed her mind after you'd invited someone in her place. I'm sure there are many better ways for you to have phrased the comment so it would have been easier for those trying to help you to have the correct information. If you're going to be this touchy, you need to put a little more thought into how you phrase questions so you get relevent responses.
If you took my post to be an attack on her, although I can't see her being overly bothered as she'll never read it, that wasn't the intention ( particularly as she hadn't invited herself). It was a warning to you that many of the
DVC owners have had similar problems in the past with relatives ignorant of what DVC involves, requires and costs. Bottom line, they often think them coming along is a zero cost to the owner ( even if the owner has to get a bigger unit) , the owner knows that is not the case but often doesn't say anything for fear of causing a scene. The situation carries on for a few years, the relative blindly believing nothing is wrong and the owners getting more and more annoyed until something gets said out of place and the whole true story comes out with both barrels. The relative feels guilty and upset that they have been accused of taking the **** and you get a massive ( and difficult to defuse) row over something that could have been sorted out with a quiet word at the beginning. It's a warning of problems others have faced in similar situations to yours. If it's not relevent then ignore it.
As previously said I don't think I or anyone else has flamed you, my own advice was an attempt to stop you from having a disaster of a vacation as I think if you go ahead you'll regret it. YOu have another 40 years + of vacations to WDW with DVC, I don't think you want to start with a trip that is packed full with potential disasters, but I have the feeling you know best, so best of luck, You'll need it.
Jim, in general I would say I tentatively agree with you. With one extra person I don't think it really makes a massive difference in the grand scheme of things as far as "wear and tear" on fixtures and fittings, extra costs on laundry (which we all have to pay) , space on busses, lack of pool space or other hotel services. But I think you are likely to agree there is a level at which if a significant number of the rooms are over occupied by 4,5 or 10 extra guests there is a time when the enjoyment of other guests (you or I) may be affected and there are financial issues alongside comfort. Disney has chosen to make the legal occupancy at those levels, IMHO with a view that there will at times be guests that exceed those guidelines. Set the limits at 4, when the resort can deal with 6 is sensible IMHO. If you set the limits at the resorts capacity (or close to it) when those limits are exceeded ( and they always will be) you are in a situation where people who have paid premium $ for a premium experience get less than they expected. That's bad for the guest, and it's bad for business.
I think you'll find that despite your initial doubts about occupancy levels ever being an issue to you, there are situations where it might be. There is a need for a line to be drawn somewhere, I'm happy that the line is at a position where minor infringements will not impinge on the experience of the members.