He (Bhismadeva) was the most satisfied man because of Yudhisthira's being enthroned in place of Duryodhana, and thus he began to congratulate them (the Pandavas)

Expressions researched:
"he was the most satisfied man because of Yudhisthira's being enthroned in place of Duryodhana, and thus he began to congratulate them"

SB Canto 1

At the last stage of his life, when Bhīṣmadeva saw his most exalted grandsons, headed by Mahārāja Yudhiṣṭhira, sitting very gently at his side, the great warrior-grandfather could not check his loving tears, which were automatically flowing from his eyes. He remembered the great tribulations suffered by his most pious grandsons. Certainly he was the most satisfied man because of Yudhiṣṭhira's being enthroned in place of Duryodhana, and thus he began to congratulate them.

SB 1.9.11, Translation and Purport:

The sons of Mahārāja Pāṇḍu were sitting silently nearby, overtaken with affection for their dying grandfather. Seeing this, Bhīṣmadeva congratulated them with feeling. There were tears of ecstasy in his eyes, for he was overwhelmed by love and affection.

When Mahārāja Pāṇḍu died, his sons were all small children, and naturally they were brought up under the affection of elderly members of the royal family, specifically by Bhīṣmadeva. Later on, when the Pāṇḍavas were grown up, they were cheated by cunning Duryodhana and company, and Bhīṣmadeva, although he knew that the Pāṇḍavas were innocent and were unnecessarily put into trouble, could not take the side of the Pāṇḍavas for political reasons. At the last stage of his life, when Bhīṣmadeva saw his most exalted grandsons, headed by Mahārāja Yudhiṣṭhira, sitting very gently at his side, the great warrior-grandfather could not check his loving tears, which were automatically flowing from his eyes. He remembered the great tribulations suffered by his most pious grandsons. Certainly he was the most satisfied man because of Yudhiṣṭhira's being enthroned in place of Duryodhana, and thus he began to congratulate them.