Probably half each until someone takes the starter spot with better play consistently for a month or so.
Once it's clear one is playing better than the other it might go to two games for the starter, one for the backup. I'd expect both to get over 30 starts, but would be surprised if either gets more than 50 starts unless an injury.
It will be a pure competition.
Thompson is the better goalie. If he stays healthy he'll end up getting 65% of the starts.