I've always been of the opinion that if its worth doing, its worth doing right. But don't take my word for it. Look at some real world examples of what might happen:
-- 2 partners get tired of the third for whatever reason and try to squeeze him out;
-- renter does not purchase insurance on their belongings, fire happens, and they sue all three of you personally;
-- 1 partner runs into some severe financial problems, house takes a huge drop in value (see 2008), all three want to sell but can't come up with how to pay for the deficiency and realtor commission;
-- 1 partner gets into tax trouble with the IRS who puts a lien on the house;
-- 1 partner has one or more unpaid judgments and a lien is placed on the property;
-- tenant who is judgment proof or files bankruptcy after trashing the place, causing 50-75K or more in repairs needed before property is inhabitable; partners can not come up with that money;
-- 1 partner gets a divorce; ex-spouse demands half of his or her equity; partners don't have cash;
-- 1 partner dies without a will and life insurance, has adult and minor children and spouse, all of which want his equity from the house, but 2 remaining partners do not have any cash;
I could go on for hours. I don't think any of these scenarios are the least bit far fetched, but if they were, you could easily change the facts a little and come up with huge potential problems. Proceed at your own risk, and remember: though I don't really do it much anymore, about 75% of my historical practice has been cleaning up one mess or another. And its cost my clients 8-20 times more than what it would have cost had they come to me in the first place.