State fire inspectors said a short on an extension cord behind the living room sofa sparked the blaze in this south Florida farming community, about 30 miles southeast of Fort Myers.
Concepcion Morales, 37, her sons Conrado and Wildred, both believed to be 17, and her nephew Gerardo ``Lalo'' Dearcia, 23, all died late Tuesday in the small front bedroom they shared.
Three other relatives were injured but escaped from the rear bedroom. All seven people lived in the 40-foot trailer, which had no smoke detectors.
Concepcion Morales' brother, Ronnie Morales, 30, was hospitalized in fair condition Thursday; his wife Gladys Hernandez, 25, was in serious condition. Their son Eduardo, 2, was treated and released.
The mother was planning to move back home to Mexico on Wednesday with her sons, family members said.