This would require a conversion from a postgres database to a local hsql database and AFAIK this is not readily available.
Using postgres locally would be the easy route, I don’t see any big obstacles to junior devs to use postgres on their local machine. I have lots of experience with people being new to Mendix that can easily handle the install and usage of a postgres database on their local machine. I think that this will outweigh the complexity of trying to get some sort of conversion between a postgres and hsql database on their local machines.