There are so many specific facts that go into answering your questions, it really is not practical to only seek advice on this forum. You need to hire an attorney that handles probate matters to advise you about your father's estate and your interest in the land and the interest of any other heirs.
Just because you have taken care of the land and paid taxes, that doesn't cut off any other legal heir who also has an interest in the land.
You may find it difficult to successfully assert an adverse possession if any other owners have consented to your maintaining the land and paying the taxes. Consent to your doing so negates any "adverseness" of your possession which is a required element of such a claim. Hard to say without knowing more (hence, that's why you need to hire your own attorney who can get into those details with you).
An affidavit of heirship may be needed if you are going to sell the property, but as you seem to realize, it does require ALL the heirs. You can't get around this requirement just because you find it difficult. In any of the ways that you might clear the title to the land, the other heirs will have to be officially notified (and in some cases formally served with process) so their interests can be recognized and dealt with.