This question is a duplicate, I know.
However the age of this question and answer is about 5 years. Mac OS and iOS updates change and so do software.
The question is again, how could I output my audio from my mac to my iPhone or iPad? The App Airfoil was suggested in the the question above however I'm sure there are better or newer alternatives.
I did check https://alternativeto.net/software/airfoil/ however I don't know how reliable this site is.
My preference of method would be over WiFi, or USB connection but anything is better than nothing.
Detailed Device Specs
iPhone 5s iOS 10.3.3
iPad 3rd Generation iOS 9.3.5
NOTE: as suggested from Streaming iMac's Audio to iPad, this open source alternative was available however it hasn't been updated. https://github.com/trenskow/AirFloat (requires iOS 9.2.1 and self-compiled with Xcode from a Mac)
Macbook Pro Retina (Model 10,1) Mid-2012. macOS Sierra 10.12.6
Even if a suggestion doesn't fit the older models above, they are welcome for others that this may help!
Thank you Ask Different community!