Difference between and usage of "Them" and "These/those"

1. 
   

   What is the difference between them and these/those?

   
   


2. 
   

   What is the usage of them and these/those?

   
   

Example sentence -

1. Some of these are insured by govt...

But I think "Some of them" is more common. But again there is nothing wrong with the quoted sentence.