What is the madhhab or religion followed by some worshippers from the Pakistani community in Kuwait who are distinguished by not completing the rows in prayer, not joining their feet and heels to the worshipper next to them, reciting tasbih during prayer, and praying four supererogatory rak'ahs before 'Isha'?

It is not possible to pass judgment on the group mentioned. Muslims in Asia are predominantly Hanbali, and they may be so given that they pray four rak'ahs before 'Isha, which is recommended by the Hanafis. Voluntary prayers between the Adhan (definition) and Iqamah (definition) are permissible, but performing voluntary prayers when the Iqamah for the congregational prayer has been called is not permissible, even according to the Hanafis. Those who deviate from the Sunnah (definition) should be advised gently and wisely, with the Sunnah explained without causing aversion.