Which towns on the Mosel ?

For landscape photographers Bremm outlook is must.

Likely you want to take pictures of Spitzhäuschen in Bernkastel Kues.

Some more tips: https://www.ricksteves.com/europe/germany/mosel-valley

Burg Eltz although the Castle in valley near the Mosel River is a huge Tourist attraction its def worth visiting and taking pictures

30km /30min from Cochem to the Carpark above the Castle
Walking down with some good views of the castle
Should be on your list

Berg Eltz is very photogenic, but a ways out from any town. The view is usually best from above on the west side, or from below. The problem is light, and crowds. This is a place that brings in tourists by the busload. As do Bernkastle Kues and Traben Trarbach.

The view from Burg Metternich, above Beilstein, will give you a fantastic panorama of the "U" bend in the river and looking out over the vineyards. The town itself is fairly small. But for a view of the town and castle you take the ferry across to the landing on the other side and find a spot from there.

The hyphenated towns (Bernkastle-Kues, etc.) are actually two towns grown together and it's not easy to get a shot of them together. Usually what you end up with is one or the other. For Traben-Trarbach climb to Burg Starkenburg (a ruin). For Bernkastle-Kues you want Burg Landshut. You'll find a lot of the towns actually have photo spots above them prepared. Bremm has two. Bremm also has a picturesque ruined monastery, Kloster Ruine Stuben, across the river.

Your brother should definitely include Trier in his itinerary. It's got loads of history, having been the largest Roman city outside of Rome itself until 400 ad. Plus it's just a beautiful place to walk around.

All of the towns along the Mosel are fairly close, but it takes a very long day to drive from Cochem to Trier along the river, because the speed limits are low and there's always traffic; much of which is backed up behind tractors, or tourists who have no idea of where they're going. The train is much faster point to point. Note that the roads into the valley are very steep and twisty, as are the trails to the vantage points or castles.

Be advised that there are over 80 castles alone in the immediate Mosel region, many of which you can be alone at when visiting. For example Burgruin Kastellaun, which is rarely visited.

[img]https://i.imgur.com/JqPrfHz.jpg[/img]

How far are you willing to deviate from the Mosel? To Koblenz to see Deutsches Eck , the point at which the 2 rivers flow into each other. If so, I suggest seeing that plus the photography from the Prussian fortress Ehrenbreitstein. The bus from Koblenz Hbf goes there.

If the historian with you is interested in seeing singular historical sites , museums, etc. in this Mosel and Rhine area, depending how far you want to drive, I would suggest Kaub am Rhein , Bad Ems (several sites there), Bacharach, plus Deutsches Eck itself.

Keep Trier for sure, it's the most important historical city of Germany (since the Roman times)

An Alternative to Burg Eltz Castle might be Schloss Bürresheim 35km /40 min north of Cochem in the Eifel Region near the Town of Mayen (with its own Castle)

Pictures to take Castle to visit and a Landgasthof nearby for lunch or dinner

Less Tourists but as nice as Eltz

Some know it as Burg Brunwald in Indiana Jones the last crusade

I know you're trying to narrow it down, but I wanted to suggest a town that isn't on the river but above the river. Starkenburg might give you both the charming streets and the long valley views. Also, ruined castle. Accessible from T-T or from Enkirch, which is where we stayed in an excellent AirBnB that I am happy to recommend. We saw no other Americans there and very few tourists at all.
We enjoyed a meal at the Restaurant Waldschenke (https://waldschenke-bernkastel.de), on the hill opposite B-K. Very near the restaurant was an old Jewish cemetery. Well signed enough that we noticed it, even though we hadn't known it was there.

In 2008, I spent three nights on the Mosel. I wanted to stay in Cochem and started making reservations months in advance for a single room. It was the weekend of a festival, Federweiß. I got many "Ausgebucht" (booked) response. All the rooms were double, and I just think they didn't want to commit to a single occupancy that far in advance for a big weekend. So, I stayed down the river in Treis-Karden. When I got to Cochem the first day, there were "Zimmer frei" signs all over town.

So, the first day I stayed in Cochem, visited the Reichsburg, and did a wine tasting at a winery there. The second day I took the train to Wittlich and a bus to Bernkastel-Kues. I had lunch there and tested some local wines at a restaurant. It was neat to say I had had dinner at ground zero for Riesling wines, but in truth, I didn't need to go to B-K; I could probably have sampled the same wines anywhere in the area.

Then I returned to Wittlich, took the train to Bullay and the bus to Zell, where I saw the statue of the Black Cat (Schwarzkatz) and had dinner.

The last day I spent at Beilstein. That was my only mistake. It was late in the season and the castle was closed. I did tour the church there, but there was not much going on. I killed time until the return bus finally arrived, drinking coffee and wine in the local cafes.

As I said, it was late in the season. and Burg Eltz was closed. I think Burg Eltz is the second worth-seeing castle in the area.

In retrospect, in enjoyed seeing Cochem and Bernkastel. They are definitely worth two days. Beilstein was worth missing, at least at that time of the year. Burg Eltz is notable for it's setting, but nearby Marksburg (Braubach), which I have toured, is a better example of a castle from that era. I don't know what I would do with the third day.

A place we enjoyed that’s not on your list is Saarburg. It has a castle that affords some good views and a small waterfall in the historic center.