Whatsapp on 2 devices is easy, they updated it with this feature, you have 1 phone be the main phone, then login on the 2nd phone as a 2nd phone, and both can access

but the main phone is still the "master" one, if you in the future need to change phones/backup/etc

https://blog.whatsapp.com/one-whatsapp-acco...multiple-phones

as for calling, not possible