It gives the impression that it's a meeting for some purpose that doesn't matters here and that there was few people present. There is a great range of possibilities and, for the sense, I dare to say it means, here, to be present: 'who had been up forward,' - 'Who had come to the meeting; who had been present in the meeting'
to be up for” em inglês, assim como muitas outras, não pode ser traduzida literalmente e pode ter mais de um significado. - https://blog.influx.com.br/o-que-significa-to-be-up-em-inglê...
be up for sth - to want to do something: https://dictionary.cambridge.org/dictionary/learner-english/...
come forward - to present oneself - https://dictionary.reverso.net/english-definition/up forward