How to close other PowerShell windows from script

I have a PowerShell script which has the following steps:

1. Opens another PowerShell window
2. Navigates to an angular projects directory
3. Runs a command to serve the project

Is there a way that I can close all other running PowerShell windows, but keep the currently running script and it's newly created window open? Following the changes, I would like it to behave like this:

1. Close all other PowerShell windows
2. Opens another PowerShell window
3. Navigates to an angular projects directory
4. Runs a command to serve the project

You could use Get-Process to enumerate all running powershell processes, then filter out the current one by comparing with the value of $PID, before piping the rest to Stop-Process:

Get-Process powershell |? Id -ne $PID |Stop-Process -Force

You can include the child process by ID if necessary:

$childProcess = Start-Process powershell $childProcArgs -PassThru
Get-Process powershell |? Id -notin @($PID;$childProcess.Id) |Stop-Process -Force

... although I would suggest simply killing all other powershell instances first, and then launch the child process after