Filebeat and Logstash are projects managed and owned by Elasic B.V. Filebeat is not open source, it falls under under a non-oss license which Elastic created. Logstash is mostly not open source either due to Elastic’s licensing, some of logstash is Apache 2.0 which is open source, hence it’s quite complex from a licensing perspective. You can get code for both components on github, just do a search.
elastic/logstash: Logstash - transport and process your logs, events, or other data (github.com)
elastic/beats: Beats - Lightweight shippers for Elasticsearch & Logstash (github.com)