Three months after the devastating death of Jett Travolta, friends tell PEOPLE about the family's struggle to heal

A few days ago, John Travolta and Kelly Preston threw a birthday party for their daughter Ella Bleu, who turned 9 on April 3, “just as they would any other year,” says a close friend of the family.

And yet this year has been marked by deep tragedy for John, 55, and Kelly, 46, who are still reeling from the sudden loss of their only son Jett on Jan. 2 in the Bahamas. Since his death from a seizure disorder, the family has remained out of the spotlight, even keeping a low profile in their adopted hometown of Ocala, Fla.

“John is a strong man, but we want to leave him in peace,” Olivia Newton-John, a longtime pal, tells PEOPLE in its new cover story. “To lose a loved one – it’s the worst time in anyone’s life.”

Still, they have slowly begun letting the world back in – starting by reaching out to those closest to them. “They aren’t secluding themselves or paralyzed,” says the family friend, who saw them recently. “[Seeing them] was like old times. Nothing awkward and no topics to dance around. There were smiles.”

Another friend tells PEOPLE that the couple are leaning on their strong Scientology beliefs and their close bonds to cope with losing Jett, who would have turned 17 on April 13.

“They’re relying on their faith to get them through this,” says the friend. “Their faith is solid, and their family is solid.” Adds their pal, actress Leah Remini: “How do you deal with the greatest tragedy in your life? I can tell you that they are handling it the best any parent could ever deal.”

For more on this story, pick up the new issue of PEOPLE, on newsstands Friday