the leaves are poisonous, don't know about the seeds, but i am still kicking, so i think they are okay...
equal parts dried elderberries, hibiscus, rosehips...for tea

Yes that is true. Some members of the elderberry family can cause nauseau or worse. The roots are often poisonous. Elderberry is in the Sambucus family of which there are many species. Research which one(s) you are working with.

p.s. I love Elderberries! ; )

I had horrible nausea and vomiting from eating dried, blue elderberries that I was moawing down on, and chewing the seeds. It lasted till i went to sleep 5 hrs later and I felt somewhat OK in the morning.

That being said, just 3 days ago I noticed a elderberry bush growing next to a campfire. I simply cut the stem below the berries, put them on a stick and roasted them till they started to drip. I ate tons of them, till my teeth got tired of it (think: eating lemons feeling), to test the "cooking them makes them ok" theory and it worked! People around the fire even tried a little.