a day boat , bike and bus trip to Melk & Krems

we plan a day trip to Melk and Krems. we think about boat from Melk to Spitz, rent bikes from Spitz to Durnstein, then take bus from Durnstein to Krems. Our questions :
1) is it possible to rent bikes at Spitz or we have to rent bikes at Melk and bring them on boat?
2)can we return bikes at Durnstein?
3)if cann't return bike at Durnstin, are there bus can carry bikes to Krem?

thanks

wei