Is there wheelchair access to the castle?

Yes

There is a wheelchair lift on the north side and an elevator to all upper floors

There is.

Yes there is a elevator on the north side of the castle

Yes there is! :-)

There did appear to be a wheelchair lift on the back side of the castle when we walked the grounds, but I would suggest calling and making sure it's for public use.

Thanks Everyone! Will take my friend based upon your quick responses.