If I move my old coins, it is the same as if I sell them to someone else, isn't it?
That would means that even if I have sold them, I still can get the new coins??
There is no difference in the way you
move coins, in new wallet under your control or to some exchange where you can sell it for fiat or for some other coin. It is only important to have bitcoin in your address in time of fork, after that bitcoin can be moved as many times as you want.
I'm personally claim only BCH, other forks are pretty worthless - but since I still have my seed where my
BTC was in time of forks it is never later to do that. In fact there are no time limit for claim such coins, the only thing that is changing is their price.