You are an intelligent guy, so my advice is, prepare for the appeal yourselves and represent yourselves.
I wouldn't trust a solicitor of that type ever, in fact I would rarely use a solicitor for any walk of life because their primary objective is £££, unfortunately client satisfaction is not high on their priorities, espcieally immigration specialists.
I would recommend you review each point, pm one of the more knowledgable posters here if required for further specific advice.
Immigration judges will factor in any evidence you present to them. If you go to court and hand over the documentation that was not presented by your lawyer, explain that the incompetant fool deliberately did not send them over then the judge will definitely consider your case. Remember the documents sent in the initial appeal are forwarded to the ECM to review.
Regarding your lawyer, don't use him anymore, it appears as if he deliberately did this, so the case would go to court. If the case goes to court, they charge extra for representation and additional time (if we
actually call it that).
That said, without knowing the 4 points, and what documentation that was missed, we aren't really in a position to advise how you go in. But please do one thing to help yourself for when your turn comes. Go tot he court where your hearing will be held, ask them when the next immigration appeal hearing is, attend one, two or even more so you know how it works, the nature of an appeal. Most importantly so you know what questions to prepare to answer. Judges unlike the UKBA officials, do their homework, so they generally only ask questions which are not covered in the application, appeal or in documentation.