Gift(s) from RELATIVES is not taxable, GIFT DEED should be prefered
therefore gift in form of gold Jewellery from your grand parent and parent will not be taxable
According to sec 49(1) your cost of gold etc would be cost of acquisition of your parent/grand parents
If you are planning to buy a residential house property AND you do not have more than 1 residential house property (other than the new one) then capital gain from selling ornaments will not be taxable . Exemption can be availed u/s 54F (conditions should be followed) , you can also go for sec 54EC by investing in bonds of NHAI and/or REC (time limit is 31.03.12)
Amount not utilized till the time of return should be deposited in cap gain a/c scheme if opting for sec 54F