The details provided above are excellent ones to use in your essay. You need, of course, a strong thesis statement to guide your writing; in this case you need a focus that will connect the three characters. As noted above, each of the young men both share traits with and contrast Hamlet. Such characters are called foils. This approach, to regard Laertes, Fortinbras, and Horatio as foils to Hamlet, could be the basis for a solid thesis and introduction to your essay.
For further information about foils and Shakespeare's use of them in this play, see the web site below.
Fortinbras and Laertes both have fathers killed by either King Hamlet or Prince Hamlet. Fortinbras takes action to avenge his father's death and reclaim the lands lost by his father to King Hamlet. Fortinbras uses any means available to him to accomplish this, including in Act 4, sc. 4, fighting and jeopardizing his soldiers' lives in order to get a worthless piece of land. Laertes immediately returns to Denmark to avenge his father's death. He wants immediate action taken or he will take action himself until Claudius calms him by telling him of a plan to kill Hamlet (Act 4, scenes 5 and 7). Both Fortinbras and Laertes are men of action. Horatio shows action when, in Act 1, sc. 1, upon seeing the ghost of King Hamlet says that they must tell Prince Hamlet and then in Act 5, sc. 2, when Hamlet is dying, Horatio says he wants to kill himself, but instead obeys Hamlet's wish that he live and tell the truth of what's happened.
One similarity among the three characters is their ability to see truth and justice when presented with it. When Laertes realizes he's been used by Claudius to kill Hamlet in Act 5, sc. 2, he immediately regrets his part and tells Hamlet the truth. Fortinbras respects Hamlet and justly honors him by having his officers bear Hamlet's body. Horatio knows what has gone on in the kingdom and honors Hamlet's wishes, telling Fortinbras he will share his knowledge.