Should I say "Ameen" individually or in congregation with the worshipers if I am unable to coincide with the Imam in saying "Ameen" during prayer, and should "Ameen" be said aloud or silently? And should "Ameen" be said once for the Imam's supplication in the Friday sermon or with every sentence, and should it be silent or aloud?

It is prescribed for the worshipper to say "Ameen" after the Imam says "ولا الضالين" (nor those who have gone astray), and to say it aloud in congregational prayers. It is recommended for the Imam and the worshipper to say "Ameen" simultaneously. If the sunnah (definition) of simultaneous utterance is missed, then "Ameen" should be said aloud. As for Friday, the Hanbalis hold that "Ameen" should be said silently after each supplication made by the Imam.