In HTF, the players in the team which has the flag, should spawn near to the flagcarrier.

That's virtually impossible the way the game has been programmed. If you're the flag carrier then just stay near your team's respawn points...

or you can manipulate the engine this like that flag carrier is/can be the spawnpoint..

by the way: spawnpoint selection would be a great feature (server side allowed ... )

add longer spawn time for those who hold the flag maybe? 1-3sec or something, but letting them spawn near flag carrier is not a good option

If they spawned near the flag carrier than it would be too much like CTF. you kill a guy and then before you get a shot off at the flag holder the guy spawns and kills you with a knife.