Since you've already asked before about whether the bonuses may stack or not, I won't go into that.
There's no need to be near the caster
Rituals don't come with any sort of "must stay close to the caster" rule unless the ritual's effects explicitly involve that. Once you complete the ritual, its effects are brought about, and that's it.
If the caster walks away, leaves the plane or even dies, ritual effects persist unless something says otherwise: Someone brought back with Raise Dead remains alive, your repaired or enchanted equipment remains repaired or enchanted, the Phantom steeds don't disappear and nor does your ability to Shadow Walk.
Shadow Walk lasts for 8 hours, and Phantom Steeds last for 12 hours or until they take damage. Neither ritual requires the caster to stay near their steeds or those affected by Shadow Walk.