Only Pence can. Well technically Pence and a majority of the cabinet or Pence and a majority of a body designated by Congress in legislation. The singular key person however is Pence.
Nobody else on the planet other than Pence can invoke the 25th (aside from Dumpy doing it voluntarily). If everyone in Washington DC from both parties except Dumpy and Pence was in favor of the 25th then it doesn't happen. I mean if everyone was in favor they could just impeach Trump instead but they still couldn't invoke the 25th without Pence.
People need to stop jumping for extreme conclusions
House Speaker Nancy Pelosi, alarmed by President Donald Trump's erratic behavior in recent days, is putting her weight behind a bill to give Congress a role in determining whether the President of the United States must be forced out of office because he's incapable of doing his job.
The move, in response to Trump's conduct in the days after testing positive for the coronavirus, would establish a process to effectively give Congress a say in removing a president from office under the 25th Amendment of the Constitution, which allows for a president to be removed from office if a majority of Cabinet members and the vice president consider him unable to carry out his duties. Section four of the 25th Amendment also says that if a majority of a body established by law, along with the vice president, declare in writing that if the president is disabled and unable to do his job, the vice president immediately becomes the acting president.
The bill, Democrats say, will create that body to help determine the fitness of the president. The proposal, which will be introduced Friday by Pelosi and Democratic Rep. Jamie Raskin, will create a body designed to "help ensure effective and uninterrupted leadership in the highest office in the Executive Branch of government," according to Pelosi's office.
The measure stands virtually no chance of becoming law. But it is designed to heighten the attention on Trump's condition after his doctors have provided limited information about his recovery from coronavirus.
https://www.cnn.com/2020/10/08/politics/house-oversight-commission-president-health/index.html
Pelosi is keeping Trump's unsuitability for the office in the headlines by creating a headline that the media will report on. She is doing what she can to keep the pressure on but she can't force the 25th.