A Delaware family has been hospitalised after it is believed they were exposed to a toxic pesticide while on holiday in the US Virgin Islands. Headteacher Steve Esmond, his wife, Dr Theresa Devine, and their two teenage sons fell seriously ill during their  stay at the Sirenusa Condominium Resort on the Caribbean island of St. John. The family were airlifted to separate hospitals in Philadelphia suffering major respiratory trauma, with 11th and ninth grade sons, Sean and Ryan, in critical care. Headteacher Steve Esmond and his wife, Dr. Theresa Devine, were on holiday with their two sons . The family was staying at the $800-a-night  Sirenusa Condominium Resort on the Caribbean island of St. John . It is believed the harmful chemical was used to disinfect a neighbouring suite at the complex the day the family arrived for their eight-night stay, 6ABC reported. The family's attorney, James Maron, said the Esmonds began to have seizures on Friday, and they were taken to island hospitals and airlifted back to the Philadelphia area by Monday. 'Their conditions, while serious, are stable and improving,' the attorney said in a statement issued to The News Journal. 'The boys remain in critical condition.' The odourless pesticide used inside a suite at the complex was reported to be methyl bromide, which is used to treat mould, insects and rodents. The Environmental Protection Agency (EPA) are investigating whether the family was poisoned by a pesticide . According to the US Environmental Protection Agency, the odourless pesticide can be fatal or cause serious central nervous system and respiratory system damage. As it is acutely toxic, use of the pesticide is restricted to outdoor use only in the United States. Investigators confirmed that the chemical was applied 'to deal with indoor bugs,' said Judith Enck, an administrator for the EPA, to USA Today. 'Their conditions, while serious, are stable and improving,' a statement from Maron's law office said. 'The boys remain in critical condition.' Steve Esmond is the administrator of Tatnall Middle School in Wilmington, Delaware, and his wife, Theresa, is a dentist. Sea Glass Vacations, which acts as a rental agent for several units at Sirenusa Condominium Resort, told 6ABC that it is aware that the family became seriously ill, but that the unit where they stayed was not treated with a pesticide. It said that pesticide was used to treat the unit immediately below the suite where the Esmonds were staying.
Esmond family began to have seizures at their resort at US Virgin Islands . It is believed methyl bromide was used at the Sirenusa Resort . Use of the chemical is restricted to outdoor use in America . Parents are in a serious condition and teenage sons in a critical state .