I would like to know if it is possible to

I'm fairly sure it is possible to decline an inheritance. I think it happens quite often when the deceased has debts, which otherwise would pass on to the heirs.

Thank you for your response.  Do you happen to know if I can gift my part to my sibling?

Yes, you can decline your inheritance, but you cannot gift it.  If it is declined then the existing heirs get your part, divided according the quota and the law. 

If I decline then are my adult children next in line? If smaller children are involved is it more complicated?  I understand that in Italian law minor children have to go before a judge to be granted a disclaimer for renouncing the inheritance.  Is this true if the children are US Citizens not Italian?