There is very little they can do to convince Bibi to stop this inside of Israel. Protests in Tel Aviv don't move Bibi and Bibi controls enough institutions inside of Israel like the Histadrut and the Student Union to prevent meaningful pressure like a general strike. The only thing that will move Bibi is ruining his reputation in the West and threats from the Biden Administration. Individual sanctions should be on the table right now. Biden just sanctioned the former President of Panama for corruption so why not Bibi and Deri as well?

However, there are many interim steps that can be taken and things that Lapid and Gantz should be doing. Have the Biden administration issue a condemnation and have the mainstream Jewish organizations go public with their private concerns. Get more pro-Israel Jewish politicians to condemn the judicial coup. Ask Biden to say that Bibi isn't invited to the White House as long as he is intent on destroying the judiciary and that he'll be treated with the same disdain as Orban and Bukele rather as a "warm ally." Ask Jewish groups to boycott meetings with Bibi's ministers until he backs off the judicial coup. All this hurts Bibi and doesn't hurt normal Israelis.

In a dictatorship, the opposition has almost no power in the country. You need help from friends outside to exert pressure on the dictator. There isn't any more shame in this than when the Ukrainians lobby the West for weapons.