Bus tour recommendation from Munich to Neuschwanstein and Hohenschwangau Castles

It's easy to get to the castles by train and bus by yourself, and you can advance book both tours together through the Hohenschangau website. And you will save a lot of euro vs a tour. I know of tours of Neuschwanstein and Linderhof, but not of Neuschwanstein and Hohenschwangau (probably because it is so easy to do by oneself for less).

Neuschwanstein and Linderhof are state owned, maybe that's why they are easier/cheaper to group together for tour companies? Hohenschwangau is still privately owned.
Either tour is too far for me for a day trip but, as Lee pointed out, the Hohenschwangau castles can be done with relative ease by yourself, and you could also spend a bit of time in Fussen before taking the train back to Munich.

We were just there and took the train from Munich for a daytrip to the castles. The route is easy and well marked when your train arrives into Fussen station. The problem we encountered was that when we rounded the corner out of the train station to walk to the waiting buses there was a MOB of Chinese tourists (hundreds) who had also been on the train with us, but decided to NOT follow the well laid path but rather just jumped down the concrete walls of the platform across the tracks and through the bushes on the other side scrambling to get to the buses.

For a new traveler it could have been a scary scene. I just stood looking in amazement as did the poor transport employees who were stationed there to attempt to guide the tourists. What a mess.

I don't think the ownership has anything to do with it. Neuschwanstein and Linderhof might both be state owned, but they are miles apart and have separate ticket kiosks. You can't buy a Neuschwanstein ticket at Linderhof (except for a season ticket) or vice versa. However, Neuschwanstein and Hohenschwangau, despite different ownership, share a common kiosk in Hohenschwangau and you can buy coordinated tickets for both castles there.

I think the real reason Greyline doesn't have a Neuschwanstein/Hohenschwangau tour is because they find it hard to compete with doing it yourself. Note: they don't have a tour of just Neuschwanstein. However, because of the vagaries of public transportation in this area, it would be difficult to put together a DIY tour of Neuschwanstein, Linderhof, and Oberammergau in one day. But truthfully, one hour at Linderhof and a half hour in Oberammergau is hardly worth it.