Greetsiel, Germany

Greetsiel, that's obscure, nobody is likely to have heard of it, you could have given us a clue ☺

Greetsiel is on the North Sea coast, near the Netherlands border. Nearest big town Emden. It doesn't have a station.
I looked on the DB (German Railways) website: https://www.bahn.com/en/view/index.shtml
I entered Amsterdam to Greetsiel. There were multiple options, presumably different bus stops, so I picked one. I used a random date. It gave me lots of options. For example:

Amsterdam Centraal dep 09:00, IC 143, Rheine arr 11:40
Rheine dep 11:56, IC 2204, Emden Hbf arr 13:25
Hauptbahnhof ZOB, Emden (Ostfriesland) dep 15:18 Bus 421, Greetsiel Hafenstraße, Krummhörn arr 16:06

Note the last leg from Emden is a bus, ZOB = Bus station.

I don't think anyone will know much about hotels in a small town that obscure. Try tripadvisor.

I can see 3 places to stay just zooming in on google maps.

Edit - and the closer I look, tons of Ferienwohnungen.

Re-Edit, Looks positively idyllic! Not too far from the the island of Langeoog and the grave and memorial to Lale Andersen, the singer who recorded "Lili Marleen".
https://www.youtube.com/watch?v=wh4qe0Hp6RU

Greetsiel is now part of Krümmhorn according to Wikipedia. HRS.com shows 3 hotels there, all with good ratings. One is an "Adults Only" hotel. I am not sure what is up that. I often travel to new places using HRS.com as my main hotel guide.

It does appear to be an attractive place.

That Greetsiel and the area around is amazingly attractive.
It has an almost hourly bus service to Norden and Emden (less on Saturdays and minimal on Sundays). Fill out »Greetsiel« on this page of the Weser Ems Bus company and you get the schedules as a pdf.
The local tourist office lists over 10 hotels.

If you are traveling at Easter, Pentecost (two holidays in Germany each) or between June and September you should book your accomodation very early in advance because Greetsiel is a popular holiday resort.

In addition to what I said in my previous post there are other times when the hotels fill quickly:
May 1 is a holiday. Many people use this opportunity to drive to the seaside from April 27 to May 1. May 10, a Thursday, is a holiday as well. Many people use this to spend a long weekend on the coast.
From May 10 to May 22 there is a school vacation in Niedersachsen (Lower Saxony), the federal state Greetsiel lies in.
From the end of June the summer vacations start in several German federal states (we have a staggering system). They are about six
weeks long. During all these times there will be more tourists than usual.

Would it be easier/faster to travel to Greetsiel from Hamburg? That is an option for us as well. We will be flying in from London, so we could fly to Amsterdam or Hamburg, and then travel from there to Greetsiel.

Hamburg airport is a little closer time-wise, 3 1/2 hours to Emden with hourly trains. From Schipol, it is at least 4 hours, but trains are more frequent and walk up fares a little cheaper. But from Hamburg airport, you can opt for all regional trains and take 4 hours with a Niedersachsen Ticket of 27 EUR for 2. DB shows the bus as being extra. In other German lands, local buses are included in the Laender Ticket, but I don't know about Lower Saxony.

If your husband's grandfather emigrated from that area, it is likely he left from Bremerhaven. There is an awesome museum there. The Deutsches Auswandererhaus (German Emigration Center). You can probably find his name on the ship's passenger list. (I found my parents' names and my name there, age 5. It was a very emotional moment.)

..looking at Google Maps, I'd probably stay at Hotel Witthus. ;)

Flying from London an option might be Ryanair from Stansted to Bremen

From Bremen 1hr30 to Emden by train and 40 minutes by bus to Greetsiel.

For a longer stay you can also check out this site for a selfcatering appartment in town near Harbour
https://landhaus-greetsiel.de/