Will iPhone and iPad both have the extra storage with the posted price for the plan

No. When you buy iCloud Storage, what you are buying is more space in iCloud to sync more data with iCloud. It cannot add memory to your iOS devices. The memory on your devices was fixed at purchase so if you need more space on either your iPhone or iPad, you'll have to delete things you don't need or use. Or consider buying newer devices with more memory.

See this link for more information --> What's the difference between device storage and iCloud storage? - Apple Support

Yes. iCloud storage is linked to your Apple ID and is available to all of your devices that are signed into iCloud with the same Apple ID.

Yes, if they're signed into the same Apple ID.

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