"You cannot go home yet."
I remember a Japanese teacher from a while back mentioning that かえる kind of implies that you're returning home and you would normally use もどる to say "return (to almost anywhere else)". Is that not the case? And if it is does it make sense to omit いえ?
Because the subject is "returning home" [いえにかえって] and the verb is "cannot do" [いけません]. The は ties them together as "returning home" is the thing that you "cannot do".
は行けません is a phrase used to forbid something; you cannot place まだ in the middle of the phrase. It should be at the start of the sentence or before the verb that is being forbidden. (まだいえに or まだかえって)
Using the volitional form implies that its something that you psychically cannot do, while in this case you are prompted to say something that you are not allowed to do.