Is possible to join in this promotion for two times?
For example:
I'll bet one BTC in each Bet and in this way I'll be able to win 4 BTC.
After this scenario, could I bet 0.1 BTC in way to win another prize?
Nope, it is one prize per person (as stated in the OP),
But you can always post higher bets than the ones you already posted to get a higher prize in the end (min. bet amount of all bets on your grid counts).