When I worked in a land titles office, I used to see this kind of thing frequently. But that was some years ago, and things may have changed. And they may differ in your location, so check everything with a lawyer before proceeding. I’m neither a lawyer nor a tax accountant, so you proceed with this advice at your own risk.
First of all, you and your brother hold title to the property. Have your brother work with you (and a lawyer) to file a deed that gives your son one-third interest in the property, along with you and your brother. We used to call this a “two-dollar transfer,” two dollars being the minimum amount that any interest in property could be transferred for in our jurisdiction. (Whether or not the money actually changed hands didn’t matter.)
Then, you and your brother file what’s called a “Quit Claim Deed,” where you both turn over the property to your son for two dollars and “natural love and affection,” as it’s known legally.
This makes the property his, (and Land Titles or the Registry Office, or whatever it’s called where you are, happy) but you still have the question of the sale money. But you and your brother and your son can arrange with a bank to have them grant a loan (mortgage, if you prefer). Your son borrows from the bank and pays you immediately, while paying the bank back according to a mutually-acceptable schedule. The sum can be whatever you and your brother decide is fair to your son.
This worked in my jurisdiction, because anybody could be granted a share in title without being charged capital gains tax. Further, capital gains were not taxed if one of the title holders “bought” the others out or the other title holders quit the claim to title, as this method uses. As far as Land Titles/Registry Office/another government agency is concerned, the deal was done for the sum of two dollars and natural love and affection.
As I mentioned, I used to see this thing all the time–transfers filed at, say, noon, and Quit Claims from title holders mentioned in the noon filing coming through at 12:05 p.m. We knew that there was some financing going on that wasn’t shown on the paperwork.
But also, as I mentioned, this worked some years ago. I no longer work in Land Titles, and I am neither a lawyer nor a tax accountant. I would seek out their advice before proceeding with a method such as this.