Welcome to RootsChat
Searching in Austria will be hard because
- many personal records (BMD certs.) are only available if you can prove you are direct kin.
- you may have to apply directly to the church or church organisation, rather than a central office. This often means you need to know the exact parish first.
There are some links on the new familysearch Wiki projekt:https://wiki.familysearch.org/en/Austria
Keep checking this page, as the project is still very much on.going and new items will appear constantly.
You say they are immigrants. A good start might be looking for naturalisation papers to see if there are more details there:
see Topic: RootsChat Topics - Naturalisation and Internmenthttp://www.rootschat.com/forum/index.php/topic,157691.0.html
Do you have their details in Britain already ? If not, then another possibility is to give us as much detail as you have, and we can try to trace them in Britain. Sometimes other family members, siblings and neighbours may provide snippets of helpful information.