You can get to the islands of Ona and Husøya by ferry or by private boat.
From Romsdal/Nordmøre:
Take a ferry from Hollingsholmen, which lies about 19 km west of Molde, to Gossen/Aukra. Then drive for about 10 km across the island of Gossen to Småge where there is a ferry connection to Ona. You can leave your car on the quay if you are going back the same way.
The ferry route Hollingsholmen–Aukra is operated by Fjord1, the ferry route Småge–Ona is operated by Torghatten Nord.
From Sunnmøre:
Take a ferry from Brattvåg, which lieas about 50 km north of Ålesund, to Harøya. Then drive for about 15 km across the island of Harøya to the island of Finnøya where there is a ferry connection to Ona. You can leave your car on the quay if you are going back the same way.
The ferry route Brattvåg–Harøya is operated by Fjord1, the ferry route Småge–Ona is operated by Torghatten Nord.
Relevant ferry timetables:
Hollingsholmen–Aukra:
http://fjord1.proweb01.nri.c.bitbit.net/Fjord1IISStaticTables/Tables/ruter/t/15-342.htm
Brattvåg–Harøya:
http://www.rutebok.no/nriiisstatictables/tables/ruter/t/15-271.htm
Småge–Orta–Finnøya–Sandøya–Ona:
http://www.rutebok.no/nriiisstatictables/tables/ruter/t/15-343.htm