Hi,
both are use in generall English as well as in legal English.
A) Will = generall English, legal English,
B) Shall = generall English, legal English.
B 1) But the meaning of 'shall' in a legal context is different, usually it expresses the meaning of must(obligation) or will (in the sense of a promise).
Every amendment to this contract shall be in written form.
B 2) Shall can also be used to refer to a future action or state.
Until one year shall have expired since ...
Best regards,
Kathrin