Elasticsearch cluster architecture

Hi guys,

As per attached diagram I've 8 application servers in 2 data centers (4 per each DC) and 4 monitoring servers przezn for ELK Stack (2 per DC).
4 app servers (1-4) push their log data to Logstash placed on Monitoring server 1 (DC1)
4 app servers (5-6) push their log data to Logstash placed on Monitoring server 3 (DC2).
Connectivity between Data Centers is not a problem. Additionally i want to have access to data from one DC when the second one is not available.

Question is:
What would be best solution to create Elasticsearch Cluster having 4 monitoring servers available ? I need to have data available for analysis in one Kibana. Could you please advise and share best practices for such a configuration ?

Thanks a lot in advance !

Ged