13,000 2 lots one church!? Help

[Esteban Camacho]

I found my first deal and it looks great!! I have two 9,000 sqf commercial adjacent lots with a 3300 sqf church on one for 13,000. The building is structurally in good condition however I'd does need quite a bit of Tlc. I am trying to buy it off three siblings who have inherited it from there father. However they have no deed and the property is in the name of the church not there father. They currently owe 10,000 worth of bad taxes witch I would pay plus I would be giving them and additional 3000 on top of that and covering all transfer fees and attorney fees as well. I understand I will be needing an affidavit to prove they have legal ownership ship before I can buy it from them. My question is how can I lock in this deal and protect my self so they can't back out after I pay all fees to have the property transferred in to there name? Can I have an attorney draft a contract even if I'm not 100% sure they legally own it? Please forgive my ignorance and THANK YOU in advance for you're help!