To add someone to the ownership requires a transfer via deed (and resulting closing and filings with the county) from the existing owners to the new group of owners (which includes the existing owners). To do it, you need someone that knows what they are doing because the deed needs to be precise to avoid later legal disasters, and a waiver of right of first refusal needs to be sought and provided by Disney. You can actually contact DVC and they can give you some information. I am not familiar with LT Transfers, but that may be an organization to contact
For MarkLT1, the transfer would be from his parents to MarkLT1 and his parents and then there could later be another transfer by deed just to him. MarkLT1 mentions his father may want to stay off the ownership when he is put on and thus he may not want to do joint tenancy with right of survivorship. Unless someone is intending to set up (and incur the expense of setting up) a trust as the owner of the property, which trust has precise provisions for distribution of the property after death, the deed to MarkLT1 and his parents, or to just his mother and him, should most definitely state that it is joint tenency with right of survivorship unless you really desire to have a costly probate in a Florida court when one of the owners eventually dies. Joint tenancy with right of survivorship means that if one of the owners dies, the others on the deed instantly become the only owners and no probate is necessary (until the last owner dies). If you do not have the deed say it is joint tenancy with right of survivorship, then it will be deemed to be tenancy in common, meaning if one of the owners dies, probate in Florida, including the cost of hiring counsel, will be necessary, and you will need to figure out who the new owner is that will replace the deceased owner on the deed, because that deceased owner's legal heirs get his share, unless his outstanding creditors grab it first.
As to the tax questions above, the are no income taxes involved with a deed transfer for which no money is passing hands between the original and newly added owners. There are the filing fees/taxes you have to pay when you file the deed with the county. The other possible issue is gift tax filings. The value of the gift would be one-third the fair market value of the timeshare if both parents and MarklT1 are on the need deed; if his father remains off the new deed, the value of the gift to MarkLT1 will be 1/2 the fair makes value of the timeshare. There is an annual gift exemption of up to $15,000 per person, meaning each parent can give MarkLT1 up to $15,000 a year ($30,000 for any gift from both of them). Thus, the gift tax filing issue is the value of the share of the property MarkLT1 receives. If his dad stays on the new deed, MarkLT1's gift equals 1/3 the fair market value of the property, if his dad stays off the need deed, MarkLT1 gets gift share equals 1/2 the fair market value. As long as the 1/3 or 1/2 fair market value does not exceed $30,000, there will be no gift tax issue. If it does exceed $30,000, there will be no gift taxes because, besides the annual emption from gift taxes, his parents also have a lifetime emption of $11.58 million each. Nevertheless, if the value of the share of property MarkLT1 receives is greater than $30,000, his parents will be required to file a gift tax return for the year, not to pay the tax but to show the possible reduction in the lifetime exemption. Of all the possible things involved in this transfer mentioned above, the one his parents should pray they should not have to do is file a gift tax return, something that normal non-accountant, non-lawyer human beings have a difficult time doing because the form consists of four incomprehensible pages that are explained in 20 incomprehensible, singled-spaced pages of instructions.