Do they need to give up their original citizenship in order to become Indonesian citizens? Do Indonesia allow dual citizenship? Here in India, dual citizenship is not permitted and therefore those who want to naturalize need to give up their original passport. That said, moving from any European country (say Netherlands) to Indonesia doesn't automatically mean a guaranteed place in the playing XI. If the player is good, then he will gain a place in the XI. If not, he need to work hard and try to gain entry.
No, same as in your country, if you are become Indonesian, you will lose your past citizenship. Exactly, now some players already removed form Indonesia National Team, such as Rafael Struick.
There is no country that does not like a good footballer especially, when he has great potentials in him. If the players that nationalized in Indonesia, because they want to be part of Indonesia national team is not worth to be included in the first eleven of the team, they will not be included. On the one hand, if they are professionals and are among the best first eleven, these players will definitely, be included to the team first squad.
I know, if they good they should be get the place, but let say if you are become a players, do you agree to join national team that will not giving or promising a place to play as starting XI? i dont think, you will agree to lose your current citizenship for new, if no promising offer. It will better just naturalized players for XI, if they are enough, so no more additional. See what happens to Struick, now he just become a players in Indonesian league clubs, that may never making him grow better, with low level league.