Thank you for posting your request on History Hub!
Family research can definitely take some time and patience. It sounds like you’ve been doing quite a bit of research and have found the records you need prior to 1940.
The name Bernhoff Bidenkap definitely revealed quite a few federal records including passenger arrival lists, census listings, and a WWI Draft Registration card but as you mentioned, the records after 1940 for Bernhoff and Muriel are difficult to find.
According to a search on Ancestry it appears their daughters Patricia and Frances Ruth later married in the Spokane, Washington area. There is a listing for both a Patricia and Frances Bidenkap having married there. According to Ancestry Patricia married a Marvin Glass and Frances married someone with the last name Darden and then later a Murray C. O’Dell. Ancestry requires a subscription but many public libraries offer free access with your library card. I would suggest reaching out to your local library to see if that’s a service they provide.
There are also a few listings on Family Search for their daughters but again not much that seems to match Muriel Walker/ Bidenkap. FamilySearch viewing is free but you do need to create an account.
In April 2022 the 1950 Census will be released which will open up additional search options. New records are released monthly on both Ancestry and Family Search so it is worth continuing to search on those sites. Contacting the New Jersey State Archives or the Washington State Archives will also be helpful as they will know what records have not been scanned but could be valuable resources that need to be searched in person.
We hope this information is helpful. Best of luck on your research!