Without the knowledge of the context of Manga, I interpret the second line of your quote as; We (or They) will focus the attack on this side rather than that sandbank.
“こっち側(がわ)” is a colloquial form of “こちら側,” meaning this side.“But I’ve never heard of “こっちっ側.” Actually a red warning line of the automatic spell checker pops up below “こっちっ” when I’m typing the word. It must be a typo, or very special parlance used in the Manga world.
The original meaning of the word '攻める' is "to attack / assault" like「敵(城)を攻める」- attack the enemy (castle) -, but it is used in the meaning of "to deal (play) with sth." like 「こちらの問題から攻めて見るか - Shall we try to play (start) with this question first? - as well today.