Presumably, you owned 25% of the home in August 1996 so you take on their cost basis for the 25% you owned or $29,125.
When your father died and his 25% portion “stepped up” to market, you each (you, brother, Mom) inherited 1/3 of his stepped-up basis or $570,000*.25*.3333 or $47,500. That gets added to your cost basis of $29,125 so $76,625.
When your mother died and her 33.33% portion “stepped up” to market (so $595,000*1/3 or $198,333), you each inherited 1/2 of her stepped up basis or $198,333*.5 or $99,167. That gets added to your cost basis of $76,625 so $175,792.
Since the sales price (net of closing costs) was $544,249 and your share is half of that, or $272,125. Your capital gain is $272,125 minus $175,792 or $96,333.
For simplicity, this assumes there were no cost improvements along the way. Including those improvements (and the math gets trickier as when the cost improvements occurred impacts the treatment given the step-ups) would reduce the capital gains.
p.s. you may want to check what is in that $544,000. That is 91% of the sales price. While 6% may be the sales commission, what is the remaining 3%? Are they all bona fida closing costs?
