we are starting a new sea of blood champain so i have some questions about the combat across the sea.

1)can the models abord the ships attack each others without using the cannon ? can they use their normal attack using standard weapons and dice?

2) models in the water can attack and be attaked by the models on a ship? if yes, the models ona ship can attack them whit standard weapons or only with cannons?

3) how can, a model in the water come back aboard on a ship? spending how much mp or fatigue?

4) when a ship go on a model in the water, the model is simple pull away, but if the model is between two ship during a side ramming?

To explain better, take page 29 of the rulebook and put an immaginary hero in the impact mark of the second picture of ramming. in that case will be the hero/monster/ model instant kill ?

1)can the models abord the ships attack each others without using the cannon ? can they use their normal attack using standard weapons and dice?

Yes

2) models in the water can attack and be attaked by the models on a ship? if yes, the models ona ship can attack them whit standard weapons or only with cannons?

With any weapon they want (standard or cannon).

3) how can, a model in the water come back aboard on a ship? spending how much mp or fatigue?

1 movement point, unless they're crossing a railing, which costs 1 extra.

4) when a ship go on a model in the water, the model is simple pull away, but if the model is between two ship during a side ramming?

AFAICT The figure is pushed ahead of the ship and onto the other one. AFAIK there are no rules for which ship gets moved by the wind first though, so you'll have tod ecide how to handle it amongst yourselves to determine which ship he gets pushed onto. In no case is "instant death" an option in the rules.