An arbiter is only required when you’re running an even number of MongoDB nodes in a replica set, to round up the number of instances to an odd number, which is required for quorum. Running more than one arbiter doesn’t add any benefit. It doesn’t increase consistency, but it does add needless complexity to your cluster.
Running more than one arbiter means you cannot use majority write concern with your cluster (as @MaBeuLux88_xxx mentioned already). Unless you’re okay with losing data, or with downtime, you should use majority write concern, and you should have at least 3 full mongod nodes in your cluster.