WOW :O I wouldn't be even thinking about lunging him, let alone riding with a hoof/hooves like that. You will cause injury to him, it won't necessarily show up as lameness immediately, but if he has a sidebone and twisted leg, you will be putting un necassary strain on his joints/soft tissue and in a few months to a couple of years he will come up unsound and there won't be much you can do about it.
Get straight onto a reputable farrier, they will probably have to trim the hoof back over a matter of months. To trim it to a normal shape immediately would be impossible and would wreak havoc on his legs. Probably he will be corrective shod as well.
With a hoof bad enough to cause a sidebone and twisted leg, you really don't want to be working him untill the hoof is as close to normal as possible and he has had some xrays to determine what structural damage has been done to his joints and pedal bone which may well have rotated by now.
Please don't work this horse yet!