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.
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Further low cloud, mist and hill fog is expected with outbreaks of rain and drizzle throughout the night.
Cloud will continue to thicken and lower through the evening, giving outbreaks of rain and drizzle overnight.
Organisers say it was a chance for everyone to remember Mylee and celebrate her life.