Yes, you can apply a set of updates atomically so they all fail or none, with conditions. No save points or nested transactions, though. And the transactions need to be grouped into a single request.
Joins, no. Most of the NoSQL systems distribute data by partitioning them on the primary key, and give you scalability by not doing any work across partitions. Which means that traditional joins won’t be supported. You can either join the application, or maintain a secondary schema that has your joined data organised in the access pattern you plan to use.
Google DynamoDB Alex DeBrie or Rick Houlihan for a ton of tutorials on how to restructure data for partitioned/distributed NoSQL systems.
