Mrs Foster died as a result of a gunshot wound to the head and a murder investigation has been launched. The second body is said to be that of an adult man but has not been formally identified, police said.
Superintendent Gary Higgins, of West Mercia Constabulary, said: "We are certain that one of the bodies is that of Jill Foster and the other is believed to be that of a man"
Supt Higgins said: "The post-mortem examination did show that Jill died from a gunshot wound to the head. Further tests are needed to try and establish a cause of death for the other body.
"The two bodies were found close to one another and the body of another dog found nearby.
"The dog has also been subject of a post-mortem examination, which revealed it too had been shot.
"Three horses and three dogs found in the outhouses had also been shot.
"Further tests are needed to establish whether the rifle found was the one used in the murder and to kill the animals."
Police said dental records were used to identify Mrs Foster's body.
A rifle was recovered near the two bodies which has been identified as a .22 rim fire rifle which was legitimately owned by Christopher Foster.
Supt Higgins said further tests were needed before it could be established whether the rifle was the murder weapon.
Police said spent and unspent gun cartridges were found scattered around the grounds of the property.
Supt Higgins said search teams had been forced to withdraw from the main part of the house last night for safety reasons.
"Concerns were raised for the safety of those in the building and the walls of the house had begun to lean in towards where search and forensic teams were working," he said.
It is hoped the search will be resumed today, police said.
Supt Higgins said it may take several days, or even weeks, to complete the examination of the house.
Detective Superintendent Jon Groves, of the force's Major Investigation Unit, who is leading the investigation, said: "Although this is now being treated as a murder, we are keeping an open mind as to the circumstances leading up to the incident.
"There has been a lot of speculation in some sections of the media, which is not helpful to our inquiry.
"Police continue to work around the clock to establish the facts on what happened at Osbaston House that morning and our thoughts remain with the families of Chris, Jill and Kirstie Foster."
Prayers were said for the family at a church service this morning, before police announced Mrs Foster's body had been identified.
Around 40 people from the Maesbrook area gathered at St John's church in the village for a Holy Communion service.
Addressing the congregation, the Reverend Prebendary David Austerberry said: "The events which have unfolded in our village this week have bewildered and stunned every one of us, not only in this community but across the country.
"It is hard to grasp exactly what has happened and it is clearly going to be some time before everything is revealed but today we pray for the Fosters and their family and friends who must be devastated by the events of early last Tuesday morning."
Last week's events have stunned those living in the "idyllic" area.
Speaking after the service, retired farmer Sandy Simpson, 82, said: "We are shocked, absolutely shocked. It's not the sort of thing that occurs in a country district like this."
Bryan Edwards, at nearby Melverley, said: "Everybody is stunned. We want to support the people involved. It's very sad."
Speaking immediately after the service Rev Preb Austerberry said: "When something like this happens in a community it stuns folk. It's idyllic Shropshire - it doesn't happen here but it has happened here.
"People are wanting to do something. We can pray for people as we always do in church.
"People have been bewildered and stunned. How can it happen here?
"They (the Fosters) had not been in the community long and were not pretty well known but nevertheless it's a tremendous shock. A small community like this always support each other."
Mr and Mrs Foster, and 15-year-old Kirstie were last seen at a friend's barbecue on Monday evening before they returned to Osbaston House that evening.
It has been reported that Kirstie may have been talking online to friends before the fire took hold at around 4am.
Mr Foster amassed his fortune developing insulation technology for oil rigs.
But earlier this year the businessman was branded "bereft of the basic instincts of commercial morality" by a High Court judge.
Court documents show that Mr Foster's company, Ulva Ltd, which had gone into liquidation, faced legal action from one of its suppliers for thousands of pounds, and also owed about £800,000 in tax.
A man who knew Mr Foster said he feared his former business associate may have "just flipped".
Terence Baines, a former director of Mr Foster's company Ulva Ltd, said: "It's anyone's guess, but it seems that the people he owed money to are big companies and I can't see them behind something like this."
Speaking from his home near Tamworth, Staffordshire, Mr Baines, an accountant, speculated that maybe Mr Foster "just flipped because the pressure of it was too much for him".
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