"bought for $450,000/- in 1995"

28 years.

Their initial purchase price + improvements (not regular repairs) = basis, and they might be eligible now for the $500,000 max exclusion from income tax on that gain from the sale. I recommend digging into the improvements, to see if there is an increase in basis. For example, it's not unusual to move into a house and "finish" it, such as that final bathroom, a nicer laundry room, a covered front entry, a pool cage or expanded patio, a real deck instead of a stoop, etc.