Site reservations

Have you checked their websites? I am pretty sure that all of these have a website version in English that will give you an up-to-date answer to your question.

For right now, expect 2G+ rules to be in effect (vaccinated PLUS tested). But who knows what will be in May or June.

I was just there in October, Dachau didn't need reservations, though if you want to go on a guided tour you'd need to get there prior to one of the two English tour time slots they had (https://www.kz-gedenkstaette-dachau.de/en/our-tour-and-programs/guided-tours-individual-visitors/). The place is very large, if you wanted to do a self-guided you could, but if you actually plan on reading everything there in the one building it would take about 4.5 hours. I'm a speed reader and went through the place with my more snail-like friend in about 2.5 hours (which at one point I just told her no way she can read all of it if we wanted to see anything else that day). If I were by myself it would take about 1.5 since I skip things I've already read about. Personally I wasn't too impressed with Dachau (the only thing worth visiting is the oven area/gas chamber/ and the religious memorials, then peering into the window where the beds were). The Museum portion has a few items (very few!- - I've seen more at museums in America), and is geared primarily towards people who don't really know what happened during the Holocaust. The place is popular with high schoolers on field trips (literally hoards of them nonstop). I almost think its better to read up about the site prior to visiting, then skip their museum displays (except the most interesting ones) and head straight for the oven/religious memorial section. You might sadly see rude people, despite signs, we saw at least one person taking an "oven selfie" (like really?), or being a super loud high school student... and we got there right when it opened.

Residenz doesn't need any reservations. Its quite large. Very fun place to visit. Give yourself about 3 hours to stroll through it. Nymphenburg has nice grounds, the main museum portion is much tinier than anticipated. It takes around an hour or so (max 2) in the primary building. No reservations needed.

As for Ludwig's lovely castles- you def have to buy tickets in advance. Keep looking online pretty much 3x per week up until your visit. Back in the pre-covid era they sold tickets up to about 6 months in advance. Now its down to around 20 days but it can vary, so you don't want to miss it if they start dropping bundles of tickets. You can no longer buy them at the center in town, though some tour operators do sell them second hand for about double the cost. If you can, try to do one castle early in the morning, and the other in the afternoon of the same day (like 9am and 2pm). Give yourself adequate time to get up to the castle and back (its a 45-55 minute hike or a 7 euro 25 minute horse ride + 10 minute walk, or a 4? euro bus ride +12 minute walk. Cash only on the bus and horse. Fussen has a strong cash-only culture so make sure you have adequate cash for dinners and lunches. There are about 2 atms in town.

"Personally I wasn't too impressed with Dachau..."

This comment may raise a few eyebrows, but I think I know what you mean. Dachau is not and was never intended to be a tourist attraction. It became a memorial site for the purpose of reminding future generations of German citizens - and others who might later find it convenient to deny the Holocaust - about the horrific events that took place here and elsewhere in Europe during the "Nazizeit." For most informed people like yourself, visiting Dachau is often an emotionally draining experience, but probably NOT so informative on the whole. Unless you just weren't paying attention at all in those classes that cover European history, there's probably very little that's new there.

Surprisingly - surprising to me anyway - many visitors and tour guides DO place Dachau high on their list of must-do's. In his 3-week itinerary suggestions for Germany, Rick himself includes a Dachau visit despite a very brief amount of time in Munich. Personally, I think there are other visits/outings within Munich's orbit that could be more rewarding and might offer new insights into Germany's history and its people.