Well what exactly are you doing, buying someone else's existing membership outright, or renting points from another member, or renting additional points from Tradewinds directly (to complete a booking you lack points for), or you can buy another membership from Tradewinds.
You can't merge points from two accounts together into one. Points stay in a membership. So you can't rent points from someone else and put them into your account. Not sure what you are trying to accomplish.
So if first one above, buying a membership from someone else, there is a fee, not sure the exact fee to transfer it to your name, but something in the $800 range. Second above is the cheapest option, and that is just rent points from someone who has an existing membership, since points do not transfer, you have to rent the entire amount you need to book a trip. No guest fees with TWs, so this is the easiest method. If you need more TWs points you can either purchase a new membership, or you can buy the required amount of point from TWs to complete a booking for which you lack the full amount of points from. Or just buy a new membership to get more points.
If buying or renting points from someone, just be sure you understand when the points expire. Ask that question.
What are you trying to do? Can you provide more details?