1.Can anyone of the 3 new kids sell it without all of agreeing to it?
2. is it the first to make a reservation gets to control the point for that year (also borrow)?
3. if 1 of the kids married (all single right now)would the spouse have a right to it if divorced (was an asset before marriage)?
4. could i have them sign a paper saying they have no legal right to book or sell or rent?
You can add adults not minors. You add new owners by actually issuing a new deed to the existing and new owners. You have to be real careful how that is done. When a husband and wife purchase a WDW timeshare, the Florida deed will say the property is being transferred to the owners as husband and wife, which creates a tenancy in entirety, which means that both must agree to any further transfer; if one dies, the other automatically becomes the owner; and debtors of one of the spouses cannot force a sale of the property to pay off that one spouse's debts.
Adding anyone else eliminates the ability to have tenancy in the entirety. What you can do is make the new deed state that its owned in joint tenancy with right of survivorship. That also means that the death of one owner simply means the remaining living owners are the only owners. One cannot sell his interests without all others agreeing. However, the creditor of one of the owners can seek to have that owner's share, and thus possibly the entire ownership interests, sold to pay off an unpaid debt, e.g., a bankruptcy court for that one owner could order the sale.
The new deed could also state that ownership is in tenancy in common, and if you fail to state it is joint tenancy with right of survivorship, it will be presumed to be tenancy in common. In that situation any owner can sell or otherwise transfer his interest to another without the other owners' permission, with the result that you could have a new stranger claiming reservation rights as a member. Any tenant's ownership share can be claimed by a creditor to pay off unpaid debts. Death of an owner means that owner's heirs get his interest.
As to control of reservations, everyone on the deed becomes a member in DVC's system and any one of them can make a reservation or cancel anyone else's reservation. If the spouse of one of the children was not added to the deed and the adding of the child was in fact a gift, then separate ownership in the case of divorce may be maintained, but there could be disputes from a divorce that have to be resolved.
If you attempt to have them sign an agreement that they will not book, sell or rent, you may later get disputes about the validity or effect of that agreement. DVC could claim that no real ownership transfer took place because you took away the material rights that are associated with ownership and, what you are really doing is just improperly creating an agreement to obtain for non-owners membership rights such as the ability to get incidental benefits. Moreover, making such an agreement creates what is called in the law a transfer for "consideration" (a form of payment from the child), and thus it is no longer a "gift," and Disney could possibly (a) insist on exercising its right of first refusal and possibly take the property, or (b) assert it is really a resale as far as the new designated owners are concerned and limit their rights as resale owners.
Also note, and I assumed it does not apply, if the existing ownership still involves a loan for the purchase that is being paid, you cannot possibly add anyone to the ownership without the lender's permission or first paying off the loan.