Ask Smithy Xtra i30 issues with remote lock

My brother's 2009 Hyundai i30 diesel began having problems with the remote door lock whereby it wouldn't lock or unlock using the remote. It would only work manually. He has had it back to the dealer a number of times, but it never happens when it's with them and they have not been able to fix it. More concerning now is that over the last two weeks the motor has just stopped a number of times while driving along. Again the dealer cannot find anything wrong with it. Any suggestions, it's dangerous to drive?