One thing I've discovered over the years, is that when you have less than 100% ownership of a rental and you elect to let the program "do the split" for you, it doesn't split everything. I find it simpler to just report only your percentage of everything and claim 100% ownership of that percentage.
For example, if you own 50% of a $100,000 rental property, you enter $50,000 as your cost basis with 100% ownership. You also enter only 50% of the rental income and expenses.
Depending on the relationship of the owners, it may make more sense to file a 1065 partnership return and issue each owner a K-1 for their percentage/share. Especially if it's not an even split, or if there's more than two owners that are not married to each other and filing a joint return. It makes one's tax life a lot easier when things happen, such as one of the owners selling their share, or dying.
