look for a new job or gather all the stakeholders, tell them that the way are pushing the team doesn't work at all, if you concede to work weekends nobody is going to reward you they maybe even be angry at you!

If you want to change the direction of the project and only if you want you because is a lot of work you should state your demands, negotiate a better compensation and only start after they put their money and compromise on the table, if not, you will get crushed and discarded and frankly is not worth it. My suggestion is that you shouldn't do a retrospective at the end of the project, you should stop it now, if they want to complete the project they should put skin on the game and not just pushing people to work harder.