Maybe it's just that picture or my eyes this morning but that belly looks off to me. A few brownish areas of concern but again it may be the picture and one should never make these judgements online anyways. Personally since this snake has an iffy background, is underweight and you say it has a spinal issue I'd think a vet visit is definitely in order. As far as feeding remember that smaller weekly meals are often healthier for your snake than large ones. Most male BP's would never need a medium to large rat a week to be in top shape and if you feed live, that's a very large and potentially difficult prey item for any snake to handle. There are a number of very good threads here about communal housing, you might want to have a read through them.