For almost all his adult life, Carlos Lopez had dedicated much of his time to caring for his intellectually disabled brother as a way of supporting his ageing parents.

Yesterday the 44-year-old was charged with murdering all three inside their family unit at St Johns Park early on Sunday morning.

Lopez is alleged to have killed his stepfather, Pablo Novosadek, 71, his mother Olga, 61, and his brother Raul, 42, before calling police to their family unit at 7am.

He has also been been charged with two counts of causing the death of an animal after allegedly killing the family's two chihuahuas.

Lopez spoke only briefly with detectives, who laid charges after they visited him at Liverpool Hospital, where he is receiving treatment for self-inflicted stab wounds.

The deaths have come as a complete shock to family friends of the Novosadek family, who could find no explanation for the killings. They said the two brothers in particular were very close.

Raul had suffered a brain injury while working as a fork-lift driver in Queensland in the 1980s. Since then Lopez had taken it upon himself to look after his younger brother, effectively becoming his carer.

Lopez managed Raul's compensation payout, although there was never any squabbles over finances and the two brothers lived with their mother at the St Johns Park unit. ''The brothers were all very close … Carlos spent his whole life looking after Raul,'' a family friend said. ''He always said 'Raul comes first.' ''

In recent times, however, family friends had become worried about the well-being of the two brothers. Raul had put on weight and was becoming aggressive, and concerns were raised about how Lopez was coping. Lopez had also taken exception to Mr Novosadek's drinking.

''Pablo was a drinker, but he was not a violent drinker,'' the friend said.

The charges came as Mr Novosadek's son, Juan Pablo, was due to arrive back in Sydney from America.

His other son, Hugo, who become estranged from the family seven years ago, spent Monday talking with detectives as they tried to piece together the tragedy.

Lopez did not apply for bail yesterday and will continue to receive treatment in hospital under guard. He will appear in Campbelltown Local Court on August 8. with Ivy Gaymer