Your father's estate should have been closed within a couple years after he died. Given what you have written, I'm guessing someone (or multiple someones) dropped one or more balls at some point, but administering the estate should have involved the gathering of estate assets, payment of estate debt with liquid assets and liquidation of non-liquid assets to the extent needed to pay debt, and the distribution of remaining assets. There should be a court order (or, with ancillary probate in other states, multiple court orders) specifying what should have been done. Given your description of his will, his real property either should have been sold and the proceeds included with the residuary of the estate for distribution or transferred into the name of your mother, your siblings and you. It should not have been left in your name.
I was put on the title of this property as the ancillary personal representative to the Estate of my father.
Exactly how is the property now titled? Use a fake name instead of your real name, and include all the words after "grants to" or "quitclaims to."
do we need documents showing this in order to list and sell?
I'm not sure what the antecedent of "this" is, but the realtor you engage can advise you about what you will need. In large part, it will depend on exactly how the property is titled.
is there a set law that we all receive equal amounts or can each one name their own amount etc.
As mentioned above, this should have been spelled out in the order closing the probate case. Since I don't know where/when the ball(s) got dropped with respect to probate, it's impossible to opine intelligently about this. However, given your description of the will, and assuming Illinois's law of intestate succession was the same in the mid-80s as it is now, your mother probably should receive half of the proceeds with you and your siblings evenly dividing the other half. By the way, if Florida law were to apply, then your mother would get everything.
it appears for legal reasons it maybe best for me to hire a probate attorney.
Absolutely.