I strongly recommend the principled negotiating strategy developed by the Harvard Negotiation Project and described in Getting to Yes by Roger Fisher and William Ury published in paperback by Penguin Books. Be clear with your objectives. Expect the Buyers to be clear with their objectives. The goal of the negotiations should be to maximize the objectives of both parties, not to see who can beat the other side. A starting point for negotiations can be a draft contract, but just because there is a written draft does not mean that the draft cannot be changed.
Word processors are wonderful things and change is mechanically easy to do.
As Buyer, you will want a fair price, the property to be in good condition, a closing date that you can meet, a way to get our of the deal if your financing blows up and other terms that you may come up with. Expect the Sellers to be clear with their objectives. Generally Sellers will want a fair price, a closing date they can live with and assurances that the sale will close as agreed. The greatest point of conflict probably will be price. Concentrate on the problem of maximizing objectives and not on personality conflicts.