[1] All coins received via address generated before encryption, B can use them also?
[2] And all coins received via address generated after encryption, only B can use them?
[3] And all coins received via address generated after encryption at A's computer (A2), A and B can use them?
Depends, if the wallet
isn't HD (Hierarchical Deterministic) (
Ex. Bitcoin Core Wallet), the answers are:
[1] Yes
[2] Yes
[3] No
Encryption won't affect the new address (
private key) generation of the wallet, any new generated addresses after the separation are randomized which will produce different new addresses for wallet A & B.
If the wallet is an
HD wallet with a SEED (
Ex. Electrum), it's:
[1] Yes
[2] No
[3] Yes
Any new Private keys are based on the wallet's seed so, if you generate more addresses, both A & B wallet will produce the same.