Particularly the British before the entrance of America. Wouldn't that have been safer and more effective than amphibious invasions in the West?

Armies need supplies. The Soviet Union would be unable to support a sudden population increase of a few million. The Normandy landing had to be supplied by a huge underwater pipeline, harbours were built in record time to carry an enormous amount of supplies by sea. Imagine the same pipeline, but stretched to Murmansk or Iran instead of Normandy. By the time such an enormous undertaking could be achieved, all secrecy around such arrangements would be gone and the Germans would be ready to meet the Western Allies, if the war hadn't ended yet by that point.

There is also the issue of pulling units away from the Eastern front. A landing in the west meant that a significant amount of units had to be moved back and forth, more forces in the east would just mean that Germany would have to do more of what they were already doing.

Plus, imaging trying to coordinate operations together when there are only a handful of bilingual speakers to go around.