What is the ruling of Islamic law, and is there any sin incurred by the spouses if the hymeneal blood does not appear during the first marital intercourse after marriage?

Once the marriage contract has been concluded between the spouses, each of them is permitted to enjoy the other in any way, and there is no sin upon them for what they do. The absence of bleeding from the hymen is not blameworthy; the bleeding may be scant or mix with other secretions and thus not be apparent. Even if it is not present at all, there is no harm in that.