@siddharth67 i tried to find a usecase for your requirements but i couldn’t find anything interesting for you. Anyways as you have succeeded in creating your own dockerfiles you can just work with your own images. When it comes to merging, just copy and paste the 2 dockerfiles into a single file and do some necessary modifications. Then you can build the image which will contain both Nodejs and Cassandra. But i cant guarantee you that it will work the way you want.
Another way is to spin up these containers using docker-compose. Its the best tool to run multi-container applications. Just go through docker documentation for more on docker compose.
Thanks.