A two-day inquest heard that the children, from Milkwall, Gloucestershire, were found dead at Pontesbury Hill, Shropshire, on July 16 last year.
All three had suffered a severe neck wound inflicted with the Bowie-type knife, while the two girls had been repeatedly stabbed in the chest.
The inquest heard that Mr Fuller, a paper mill worker who had a degree in molecular biology, drove the children away from his marital home on the morning of July 12 after agreeing to split up with his wife.
During the inquest, Mr Barkley heard that Mr Fuller's wife, Ruth, had been suffering from mental problems and attempted to stab herself and take an overdose after the children left.
More top news
It will be a cold and frosty night with showery and wintry spells, clearing to a dry Sunday.
Big celebrations for one couple and their families after they got married - in a busy shopping centre !
Five NHS trusts in the Midlands have come under fire after it emerged bosses were sitting on more than £134 million of spare cash.