Dear Subhasree Ramarathnam Chelladurai, there is no general rule on this. You are free to publish the Full Paper in a different journal that is perhaps better suited or has a higher impact factor. However, the original journal that published the conference proceedings perhaps plans for a Special Issue dedicated to the conference. In that case I would suggest to stay with this journal.
Better to publish in different journals. Firstly if you submit many MSS in the same journal it will take time to get published. If your selected journal is good, not necessarily all your MS will be accepted for publication. If you publish in different journals you will come to know about the difference in quality of reviewing and editing in different journals.