Absolutely brain dead idea of Slys, makes zero sense and will either be ridiculously expensive as structural engineer/council/real architects should be involved then cost for all the steels because his stupidity appears to be motoring through supporting walls or it will be done on the cheap and result in serious structural damage to the whole house.
If I liked the man I’d say don’t be a dick and just put the stairs back where they should be, the tiny awkward bulkhead corner of your dog crated hall will not lose anything aesthetically, the property was built to accommodate the cellar stairs in that location and thus will be a simple and relatively cheap replace, whilst maintaining the structural integrity of the property, BUT, he’s a knob so I’m gonna say, go for it Sly, it’s a fabulous idea and will offer so much more to your house, defo increase it’s value and saleability, want give you loads of pointless hall ways down in your cellar and will be an absolute bargain