http://www.svar.ra.se/http://www.arkivdigital.net/ - lots of records online, these sites need a subscription.
Can you confirm:
When, where, and under what name he entered the US
His birthdate - he may have been born later than 1881? Dates seems to vary although if I have it right he may have lowered his age when he married Melita.
It does appear to me that there were two Andrews of a similar age, which makes things tricky:
1. Andrew Hillstrand, m. Marie b. Sweden - in 1910 and 1920 in ND with daughter Zelda
2. Andrew Hillstrand m. Mary b. MN - in 1910 onwards in MN with son Melvin
One of these (ND Andrew as he has a WWI record with right birthday but 1883 not 1881) appears to then move to California sometime between 1920 and 1930, along with (second?) wife Melita.
https://familysearch.org/pal:/MM9.1.1/K8NC-VDK - here is the marriage to Melita. It does give his parents but only as "A Hillstrand" and "Bessi Jackopson".
Interesting that he lists himself as single - although birthday is consistently 16 Jan for both WWI record in ND - wife Marie in Bismarck - and WWII - wife Melita (place of birth FALUN, Sweden on this record)
The spelling Hellstrand does appear in Sweden. I think "Hellstrom" may be a red herring (unless you have a confirmed record of him which uses it).