(a) Joint lives, for purposes of credit life insurance written under Insurance Code Chapter 1153, mean only spouses or business partners, and such persons must be jointly and severally liable for repayment of the single indebtedness and be joint signers of the instrument of indebtedness. Endorsers and guarantors are not eligible for credit insurance coverage. Joint life coverage may not be written covering more than two lives. Jointly indebted persons may not both be covered separately at single life rates.(b) Joint life rates may not be charged for single life coverage.