Possible Clues:

• Large pimple on face or neck
• How your relative might boil under Car B
• Diamond perhaps not being worn by relation - a cheaper jewel?
• This sore stone might smash a crab over 7 down
• Cluster of boils - jewel
• Sort of boil; a gem
• Red gem
• Gem of a vehicle used by bachelor relative
• Severe abscess in the skin
• Red stone making for an architectural monstrosity