Ricardo, that is very good question, and many people asked it before.
There were many ways to get to Humburg, and two of them you mentioned in your message were valid means of transportation in these years.
Also they could go by train. The city in Romania Galats was connected with other European countries, and Ismail is not that far from Galats, only 60 miles.
The other way possible is thru Kishinev, although it is longer way to Kishinev, but Kishinev was connected to European countries via Yassy.
I would think that the ship option from Ismail to some of European countries on Danube is more likely.
I never find any records of these travels, only in people's stories I saw that some went to Odessa, etc.
All the best,