So, I think I have found Hilda and Augusta. If these are the right pair, they were nieces of my GGGmother, not cousins. I have one problem though - the församlingsbok for Dagsås parish ends in 1899, so I can't follow the family forward to when the sisters would have emigrated. In the past, I have had luck searching at the county level for more recent records, but the församlingsbok for Halland SCB also ends in the same timeframe. Is there somewhere else I should be looking?
The sisters are Hildur Gerda Maria Augustsdr b. 13 Apr 1888 in Ås, and Augusta Charlotta Augustsdr, b. 6 Apr 1894 in Dagsås. Parents were August Andreasson and Charlotta Gustafsdr (who was my GGGmother's sister).