WP-Members not populating data

You’re integrating the native WP form, which the plugin can/does do. I looked and you do have the components there for it to successfully register (it would be looking for the “wp-submit” value which your form does pass.

If your custom fields are not being populated, then you probably need to look into whether you are running something that hooks to the user_register action. The WP-Members processing for custom fields is hooked to that action at a priority of 10 (the default). If you have something like a redirect hooked to that, you may be exiting the process before all other actions are completed.