To BOX2 from BOX1
$ mosh BOX2 # worksTo BOX3 from BOX2
$ mosh BOX3 # worksTo BOX3 using BOX2 as a jumphost (from BOX1)
$ ssh -J BOX2 BOX3 # worksTo BOX3 using BOX2 as a jumphost using mosh (from BOX1)
$ mosh --family=all --ssh="ssh -J BOX2" BOX3 # does not work!