It was unclear how the family died and neither homicide nor suicide could immediately be ruled out, said sheriff's Lt. Erin Giudice. She said there was no threat to the community and deputies were not searching for any suspects.
The handguns were found near the bodies of a man and woman in their 40s or 50s who were discovered together Sunday in a downstairs closet, Giudice said. The bodies of a woman in her 70s and two sisters in their early 20s were found in the attached bedroom, she said.
One of the guns was registered to the woman found in the closet, Giudice said.
The man appeared to have suffered a gunshot wound, but it was impossible to tell if the others had been shot as well because of the advanced decomposition of the bodies, she said. Authorities believed the bodies had been in the house for two to three weeks.
"The bodies were terribly, terribly decomposed," she said. Investigators wore breathing apparatus while searching the house for evidence Sunday evening.
The coroner started autopsies Monday morning but Giudice said the procedures wouldn't be completed until Tuesday. Identities of the dead wouldn't be available until Tuesday because of the difficulty of examining bodies in such advanced decomposition, she said.
Giudice said deputies were called to the home twice in recent weeks - on May 14 and Saturday - by concerned neighbors and family members, but in both cases the callers thought the family might be on vacation.
Deputies didn't enter the house and saw nothing amiss. Police generally can't enter a home in such a situation unless they see something suspicious.
Deputies called a locksmith on Saturday to get into a car parked in the driveway for an unsuccessful search for a garage door remote.
On Sunday, the relatives broke into the house and found the bodies, Giudice said.
The house is in Sea Pointe Estates, a gated community of about 75 upscale homes on a hill near the coast in San Clemente, about 65 miles southeast of Los Angeles at the southern edge of Orange County.