You really ought to speak to an attorney about this - there are many different issues here for many different people. there is a lot at stake, and as you indicate many of the questions are unclear or confusing.
1) I wouldn't. In theory each case can be in a separate envelope within the main envelope, but I would send each separately.
2) Well, they don't need to surrender their visas, but they may find that they have difficulty entering the U.S. on visitors visas - which require the intent to visit briefly and then return to their home abroad - once a green card case is on file.
3) since you are a citizen, you leave 14/14b blank - they don't apply to you. C17: Yes, I enter the names of all relatives. 18: they will likely stay with you until they locate a place, right? So your address will be correct here. #22: you would only complete the lines on the right side for relatives living outside the U.S., using the city nearest them with a U.S. consular post that processes immigrant visas. For your sister, it will be many, many years before you would be able to file the I-485 for her (same for when your brother will be able to come here). section D #1: Yes - everyone for who you are submitting I-130s.
Incidentally, you do know that, as long as your parents are still married, you only need to file an I-130 for one of them, right? The other can accompany as a derivative spouse (the only risk is that if the one you file for passes away, you would then need to start from the beginning with the other parent).
Speak with an attorney before filing.- there are many other potential pitfalls here.
No they cannot in most cases enter the country once the I130 is filed. No you cannot submit the I485 until there priority date is current. Again I know you are trying to save money but you should not be doing this on your own. The fact that you are questioning filing the I485 shows this is too complicated a process for the inexperienced and it is. It should be handled by a professional. I have a number of clients who have come to me after trying to do it themselves and all they did was slow and complicate their situation. In addition they end up spending a lot more money in the end and are completely stressed out. You can take this risk yourself but if you would like a free consultation and affordable estimate give me a call.
212 537 4407