This is a tricky one. Some general guidance below, but I also recommend getting a tax advisor to crunch the numbers for your exact situation. It’s been over 5 years since I sold a rental.
Plus there may be other factors, such as phase outs, AMT, etc that come into play. Also, note that some rules were changed over the years. If this has been a rental longer than about 10 years there may be substantial differences in depreciation rules, etc that were grandfathered into the law.

First, the basics …
Capital Gain on the property is:
Sales price minus the following:
a) selling costs, including commission, etc
b) Cost Basis

Cost Basis is the original cost of the property, plus any improvements, minus depreciation.

The tax on the gain is then split into two parts: Depreciation recapture and capital gains. The amount of the gain that is due to depreciation recapture is taxed as ordinary income up to a maximum rate (I believe it is 25%, used to be 28%). The capital gains is taxed at cap gains tax rates (typically 15% for long-term gain).

The issue of offsetting capital gains with capital losses is straightforward for the capital gains on property. He can apply this against other capital losses. Since the portion that is due to depreciation recapture is technically considered ordinary income I am fairly certain that he cannot use this to offset capital losses.