Complex sentence: His family converted to the Anglican faith in the late 1700s, amongst the first Jewish families to do so, to be able to serve in official capacities within the British power structure, then prohibited to non-Anglicans.
Split into simpler sentences: His family converted to the Anglican faith in the late 1700s and were amongst the first Jewish families to do so. This was in order to serve in official capacities within the British power structure, then prohibited to non-Anglicans.