Droves of grief-stricken teens began arriving Sunday afternoon to pay their respects to slain sisters Isabella, 15, and Maria Perez, 14, who authorities found shot to death alongside their stepfather inside a Katy home after a possible murder-suicide.

The children came with flowers and heartfelt condolences penned on cards and posters. They hugged, cried and consoled each other under a tree at the home where the Perez sisters lived in the 3800 block of Silver Hawk Drive.

After learning of their death, Mayde Creek High School student Catalina Silva, 14, said she woke her parents up in tears. She had known Isabella and Maria since the 3rd grade and each memory, she said, was precious.

She last saw the girls, who lived down the street from her in the Westfield subdivision, after school Friday to get a pep talk from them.

“I keep thinking about our last moments together,” Catalina said, crying alongside her mourning friends. “They were cheering me up because I was going through some stuff.”

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The sisters were close and their friends described being friends with both of them.

Joe Lopez, 14, who had been dating Maria for more than a year, brought a toy soccer ball to add to the memorial because she loved sport.

He said Maria had dreams of being a model. She was slated to celebrate her birthday next Saturday with a party, he said.

Another teen in the huddle outside the home said she had been there since 9 a.m as police were wrapping up their investigation. News of the slaying quickly spread on social media, where 14-year-old Jessica Hernandez found out her best friend, Isabella, had been killed.

“Everyone was posting about it in Snapchat and Instagram. I didn’t believe it,” Jessica said, after being dropped off by her mother. “I cried, mostly yelled, not believing that it was true.”

Deputies made the tragic find in an upstairs bedroom after a pre-dawn phone call from the teens’ mother, Harris County Sheriff Ed Gonzalez said.

The mother, Reyna Isabel Perez, was unable to find her daughters or husband after returning home from a night out around 3:30 a.m. and phoned police, according to authorities. Deputies found the teens and their stepfather, Victor Portillo, shot to death in the bedroom.

The slayings were “likely a murder of two and suicide,” Gonzalez said, attributing their deaths to a possible act of domestic violence. There was “no reason” to believe neighbors were in any danger, he added.

He did not elaborate further on the nature of the domestic violence. Harris County records show Portillo owned the home where he and the girls died.

At times, Isabella hinted to her pal that something was not right in her family.

“She always said there were problems but she could never really talk about it,” Jessica said. “It was too hard for her. I didn’t force her to tell me anything.”

She has tried not to think about what led up to the shooting.

“I haven’t really focused on that. Mostly on the thought of them not being here, that I can’t see them anymore,” she said.

When the teens return to Mayde Creek High School on Monday, they plan to honor the sisters by wearing red and black.

A next-door neighbor said she did not hear the gunfire and only realized something was wrong when she woke up and saw police investigators outside.

“I don’t know if there would have even been anything we could have done if we had heard the gunshots,” the neighbor said, declining to identify herself.

It’s not clear when the three were shot, but Gonzalez did say that the slayings likely occurred inside the home. Initially, he said it was “wide open in terms of what could have occurred.”

The murder-suicide investigation in Katy was the first of two domestic violence-linked slayings the sheriff’s office was looking into Sunday. In the second, a man and woman in Tomball were stabbed to death after an argument with the woman’s estranged husband.

The husband, Brian Bullock, 34, later turned himself in and was charged with capital murder.

Gonzalez tweeted that even though October was Domestic Violence Awareness Month, “let’s not forget this is an issue going on all year.”

He characterized domestic violence as “a deadly issue that affects so many lives in our community.”