It sounds like your father made you joint tenant on his Illinois property, perhaps to avoid probate. He and you likely expected you to share the property with others when he passed.
He may not have realized that as joint tenant with the right of survivorship, you became the sole owner of the property. If you divvy it up now with the intended beneficiaries, some major taxes could likely hit you.
One thing you may want to consider, as explained by the Illinois State Bar Association, is a resulting trust. Illinois law allows for the creation of such a trust when you receive an asset, if you did not pay for the asset, and if you took it with the understanding that you were merely holding it for the benefit of others.
Initial presumption of a gift between father and child
While Illinois law assumes that a transfer between your father and you would be a gift to you, you can defeat that assumption. You must demonstrate the intentions of the family to the contrary.
Demonstrating it's not a gift
You will want to show that you did not pay for anything related to the property. Not only did you not pay for the property when your father transferred it to you, but you also did not pay any of the subsequent taxes or maintenance of the property.
This is because if you were not taking real ownership, but just holding title, you would typically not be paying the carrying costs of this property. Also, proof that you were trying to help your father avoid probate can help show that there was no intention for the property to become your property and not your father's while he was living.
Your only intended interest is in the temporary title and subsequent distribution according to your father's will. If the court will allow the creation of a resulting trust as an operation of the state's law providing for this, you will keep title in name only, and be acting only as the trustee.