25p and 50i confusion

I'm shooting for an ad film to be aired on TV. During my first shoot today I shot at 50i, while reviewing the footage I realised my camera's 50i footage has a lot of moire. If I want to mix a few 25p clips (which I'll shoot tomorrow) with a few 50i clips, will it be a problem while editing?

Depending on your NLE you ate editing in you should not have an issue putting 25p in a 50i timeline. The NLE should just manage fine. If not you'll need to transcode the 25p footage.