Yes he is free to lobby for beneficial new law, though it likely will not affect his pending litigation. In most cases, new law is applied only prospectively, so it will not affect causes of action that arose before the new law was passed. That said, there is probably no legal barrier to your brother seeking a change in the law. In fact, there is a private quasi-immunity called the Noerr-Pennington Doctrine that specifically protects citizens from liability for most actions arising from their lobbying efforts. This quasi-immunity is often specifically applied where the new law sought is anti-competitive or otherwise detrimental to ones competitors.
Based on the limited facts you provided, yes. Simply asking the legislature to consider a change in the law is not improper. We all have a right to advocate for changes in the law. Nevertheless, if your case is ongoing you should consult with an attorney. Good luck.
This answer is not intended as legal advice and does not establish an attorney/client relationship.
You can ALSO try to change the laws if you wish.
The Republicans do it all the time.
THIS ANSWER IS PURELY FOR ACADEMIC DISCUSSION ONLY AND DOES NOT CONSTITUTE ANY TYPE OF LEGAL ADVICE OR LEGAL REPRESENTATION.