I have various cameras 2 X 4K 30Fps and 1 X HD 1080 30Fps and 1 X HD 25 Fps
Question is I have a 4K UHD 2160 30Fps timeline and have tried a test with starting with a 4K clip then a HD 30 Fps then a HD 25 Fps and they all played OK then I rendered to MP4 clip and played and looked OK should I be doing anything else particularly the 25 Fps clip ?

Best would be that all framerate are the same or to be divided by an integer like 2,3,4. Timeline should reflect the final render size. If the 25p plays OK on the final file then let it as it is.