Guðmundur Sigurðsson, b. 1836 was the son of Sigurður Benediktsson (1796-1859) and Steinunn Oddsdóttir (1807-1869) Sigurður lost his first wife (Sólveig Árnadóttir) in 1835, and married his second wife (Guðný Jónsdóttir in 1836) - Guðmundur was born in between, so to speak.Steinunn Oddsdóttir had 7 children with 4 men, but never married
Sigríður Jónsdóttir, b. 1850 was the daughter of Jón Þorvaldsson and Una Gissurardóttir, who lived at various places in Skagafjörður, mostly in Reynistaðir-parish.
My records actually say Sigríður died in 1882, but that may be a case of mistaken identity - please let me know if you have any information about her emigrating.
And yes, once the Gardar book is out, I need to know where to buy it - please keep me informed.