Nicola and 49-year-old Brendon James Perry died at a property on Parkers Road in Tāhunanui on 4 September.
RNZ understands their deaths are being treated as a suspected murder-suicide.
The alarm was raised after a shotgun was stolen from Hunting & Fishing on Quarantine Road in Annesbrook.
In a message accompanying the fundraiser on Facebook, Schroder said her family was trying to cope with the loss of her sister, and she wanted to help her nephews.
“My family are trying to cope with intense grief from the tragic loss of my sister Nic Perry, and right now the best way I can support my nephews is to help their futures, Nic would have wanted us to.”
The fundraiser page said the money raised would go towards providing Ryan and Josh with a safe and stable home, as well as supporting their future schooling and study.
The fundraiser has raised more than $12,000 for the family so far.
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