he brother of David Haines and wife of Alan Henning have written a joint letter calling for "acts of unity" against Islamic State (IS) militants.
The men were both killed months after being kidnapped by IS in Syria while on aid missions.
The letter condemns "those who seek to drive us apart" and urges all religions to find "a single act" in the coming weeks that "draws people together".
A memorial service is to be held for Mr Haines in Perth, where he grew up.
Mr Haines's brother Michael will address family, friends and colleagues of the 44-year-old at the service on Saturday - which will be held five weeks after his murder.
A book of condolence has opened in the city for the father of two, who was taken hostage in Syria while working for international relief agency ACTED in March last year.
Mr Henning, a 47-year-old from Eccles, Greater Manchester, was captured in December while on an aid convoy in Syria.
Hundreds of people attended a memorial service for Mr Henning last week, while Prime Minister David Cameron this week said he would consider recognising the murdered aid worker with a national honour.
David Haines A memorial service will take place on Saturday for David Haines, the aid worker killed by Islamic State militants
In the letter, Michael Haines and Barbara Henning said their loved ones had been delivering "vital humanitarian support to those who needed it most".
"Their desire to help was not driven by their religion, race or politics but by their humanity. David and Alan were never more alive than when helping to alleviate the suffering of others.
"They gave their lives to this cause and we are incredibly proud of them," the letter said.
The pair said they had come together to write the letter because "we will not allow the actions of a few people undermine the unity of people of all faiths in our society".
"Together we have the power to defeat the most hateful acts. Acts of unity from us all will in turn make us stronger and those who wish to divide us weaker," they added.
'Simple acts of unity'
"We condemn those who seek to drive us apart and spread hatred by attempting to place blame on Muslims or on the Islamic faith for the actions of these terrorists", the letter continued.
"We call on all communities of all faiths in the coming weeks and months to find a single act of unity - one simple gesture, one act, one moment - that draws people together.
"We urge churches, mosques and synagogues to open their doors and welcome people of all faiths and none.
"All these simple acts of unity will, in their thousands, come together to unite us and celebrate the lives of David and Alan.
"This is what David and Alan truly stood for."
Mrs Haines and Mr Henning said they had been "overwhelmed" by messages of support from within the UK and around the world.
Alan Henning Alan Henning was on an aid mission to Syria when he was kidnapped and later killed by IS militants
In a separate video message, Mr Haines said he wanted other families to understand that terrorism and extremism was not "something that happened to other people", adding: "It affects us all."
"Together we have the power to defeat the most hateful acts," he said.
He said his brother was an "ordinary guy from Perth who did extraordinary things".
"My brother's killers want to hurt all of us and stop us from believing in the very things that took David in conflict zones," he said.
"My brother didn't see nationalities or religions, he just saw other human beings in need of a little help to get by - or sometimes a lot of help to live to see another day.
"This is how my family will remember him," he added,
IS has killed two other Western hostages in the past two months - US journalists James Foley and Steven Sotloff - and is holding the British journalist John Cantlie, who has appeared in a series of propaganda videos.
www.bbc.co.uk/news/uk-29668473Too good to excerpt.
