A. When people talk about retirement portfolio, they typically refer to stocks and bonds and the allocation between them. If you also own rental properties, you could treat your rental property holdings as stocks (in other words, put the value of your rental properties into the value of stocks category when calculating your portfolio allocations).
The reason is you could treat a rental property just like a stock that pays dividends. Like a stock, your property's value could be up or down, and your rental income might be interrupted due to issues with your tenants, just like a stock if its underlying business falters, all these uncertainties make the renal property more like a stock then bonds. Furthermore, a rental property's poor liquidity makes it worse than stocks.