Laertes and Ophelia deserve as much sympathy as Hamlet. At first, Hamlet is the main victim (in addition to his father) in Claudius' plot. However, as Hamlet sets his plan for revenge into action, Polonius, Laertes, and Ophelia become victims as well. The result is that mental battle between Clauduis and Hamlet leads to Polonius' death, Ophelia's suicide, and Laertes' death.
Keep in mind that Hamlet loses his father. Hamlet's killing of Polonius is accidental (he thinks Polonius is Claudius), but the result is that Ophelia and Laertes lose the father. So, all three (Hamlet, Laertes, and Ophelia) each lose their father. By this fact alone, the siblings deserve as much sympathy as Hamlet.
Ophelia's depression is brought on by Hamlet's behavior and the death of her father (killed by Hamlet). Hamlet alienates Ophelia by using his "madness" strategy, thereby alienating his beloved, but it is his own doing. When Ophelia kills herself, Laertes is grief-stricken and so is Hamlet. Although Hamlet's grief is real, it is perhaps easier to sympathize with Laertes since Ophelia's death was a product of Claudius' and Hamlet's actions.
Hamlet is a victim of Claudius' schemes. Laertes and Ophelia are victims of Claudius' and Hamlet's schemes. Hamlet's schemes are more justified than Claudius' but in the end, Laertes and Ophelia must deal with death and loss just as Hamlet did. Therefore, they deserve sympathy as well.
Well Ophelia first of all is shown as oppressed. Hamlet says he loves her and then hates her and he insults her so she goes through verbal and mental abuse. In the end when Hamlet kills her father, she loses all sense of her sanity and attempts to kill herself. Hamlet becomes a tool in the hands of Claudius and Ophelia and Laertes were used as tools in both the hands of Claudius and Hamlet. This story is for sure one of the best epitomes of betrayal.