Properties full paid off. Sell, refi, or borrow against equity ?

Looking to go for my first real estate transaction. And I have a semi vague question. My father and I plan on doing a syndication. He owns three single family properties free and clear ( bought them dirt cheap when he was 20) at first I had thoughts of selling one to use as down payment on a multi-family property. But the more I think about and learn, I'm just wondering if it would be better to just refi/borrow against equity, on one or multiple of the three properties to get the down payment ? I don't have an exact property lined up just looking at a few in the 200-400 k ballpark. Thanks