Yagyu Shinkage-ryu at Kenzen Dojo is a branch of the Yagyukai, run under the auspices of Yagyu Koichi, 22nd soke of YSR. He comes to New York once a year to view and instruct practice.
The Marobashikai split off from the mainline in the 1970s. It is run by Watanabe Tadashige, the son of Watanabe Tadatoshi, who was a high level student of Yagyu Toshinaga, the 20th soke. I don't know
The curriculum is essentially the same, just arranged a little differently. The Marobashikai website calls the different levels of the curriculum "ranks", but we don't really have this concept in the Yagyukai. You practice until the soke decides you should learn the next kata. There are no tests, no ceremonies. You are simply shown the next kata and start to practice it.
With three generations separation there's some differences in the physical expression of the ryu.
Josh Reyer
Swa sceal man don, žonne he ęt guše gengan ženceš longsumne lof, na ymb his lif cearaš. - The Beowulf Poet