I am still confused as to what you are trying to achieve now you've thrown the MiFi router into the equation too.... can you not be a bit more specific?
Either way, a few thoughts to put out there in case they help:
MiFi router - iPad and iPhone should be able to connect to this and use the data connection, likewise laptop etc. could connect to it too
iPhone - if you have tethering in your price plan then you can activate the personal hotspot and then connect the iPad to this hotspot so you an use the phone's data connection on the iPad. Again, same applies to any other device e.g. laptop you want to tether your phone to in order to share the data connection
iPad- I'm not sure there is a personal hotspot option (don't think there is on my iPad 1), so nothing will be able to connect to the 'wireless' of you iPad. If there is an option for personal hotspot on your iPad then you could connect e.g. your laptop to it in order to use the data connection
Does that help?