So I want to trade ed e for cass but not sure if i want to keep cass over ed e. ifi dismiss a companion can i go back and retrieve them later at the place where i first seen them?

yup after u dismisses a companion there will be short message saying the whichever companion is back in where they were found

Do they just tele to original place found or walk just want to know because if they walk there could be risky to dismiss them far away from where they need to go.

You can have ED-E and Cass at the same time... and they do go to their original areas until you get a presidential suite at the Lucky 38. Then they go there.

after the patch I'm not getting the option to send them to Lucky 38 anymore. This happen to anybody else. Not a big problem, but a bit annoying.