Thieving Sisters

If someone is receiving benefits and is being given cash gifts from a relative - do they have to declare this? Is there a limit to the amount they can receive before it affects their benefits?

If cash gifts have been received from a parent prior to them passing away and their estate is under the inheritance tax threshold - do the gifts have to be declared and is it the responsibility of the individuals who received them or the person dealing with the estate (there is no executor as there was no will)?