IBI is the local Council Tax on a property and you will only get one bill, 360 euros pa sounds about right for 2 beds.
Perhaps your wifes name was first on Notary documentation when completing, surprisingly they only seem to use one name even when in joint ownership.
Be aware of the final payment date on the form as fines will be automatically levied if not paid on time, I believe you can get dd forms from town hall or some banks may be able to oblige
Interesting that Phase 1 bills are just being sent as most of Phase 2 had theirs last November.
Unlike government La Renta Tax which is yearly tax on each individuals assets and property where both of you will be expected to pay a proportion using form 210 or your solicitor will file on your behalf.