Can I participate in group (my group includes 2 persons) ? or only one person can participate?
A group can participate – however subject to available funds only one winner may be invited to the conference and expenses paid.

Which material do I need to submit? (Only the abstract or also the source code and others)
You need to submit sufficient materials for the judges to validate your submission. Depending on what you are submitting that could include source code. For a software submission you must submit something that runs (could run over the web) by May 15th. Source code must be submitted (it must be an open source project (e.g. Source Forge).