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Contact your operator and ask if they support multiple active SIMs, by default any old SIMs are deactivated when you issue a new SIM so it all depends on the operator.
All apps can be synced between phones, you can even use NFC pairing during initial setup of the phone to copy all Google details from the old phone, including apps, contacts, etc.
WhatsApp will log off from one phone if you use the same number to sign in another phone.