No, currently there's no way to do that except to retrieve the whole list and do your own sort. The idea is that parameters on various lists of lenders should be consistent, i.e., "newest" should mean the same thing whether you're getting a list of lenders who are members of a given team or a list of members who are, let's say, lenders to a given loan. I filed a team join time sort parameter as a feature request, but it probably won't be prioritized any time soon. Will the workaround be usable for you for the time being?