Checkbox to edit specific sheets when macro is run

I ran this macro to assign a linked cell to each checkbox, uses the cell the checkbox is on, you can set the text color to match the cell colors so the true and false are not visible.

Sub LoopThroughFormCheckboxes()
    Dim chkbox As CheckBox
For Each chkbox In ActiveSheet.CheckBoxes
    With chkbox
        .LinkedCell = .TopLeftCell.Address
    End With
Next chkbox
End Sub

Altered your sub to this.
Hopefully you can follow the comments

Sub AddMembers()

Dim rng As Range, cel As Range, sStr As String
Dim Ws As Worksheet, wksheets As Variant
Dim i As Long, c As Range

'Loop through each check box linked cell
Set rng = Sheets("dates").Range("J2:J13")

' build a string of month names
For Each cel In rng
    If cel.Value = True Then
        sStr = sStr & "," & MonthName(cel.Row - 1, True)
    End If
Next cel

' split the string to get array of month names
wksheets = Split(Mid(sStr, 2), ",")

' loop through the array of month names
For i = LBound(wksheets) To UBound(wksheets)
    On Error Resume Next    'in case sheet doesn't exist for that month
    Set Ws = Sheets(wksheets(i))
    On Error GoTo 0         're-instate error notifications
    
    If Not Ws Is Nothing Then   'if that worksheet does exist
        
        'test members
        Sheets("dates").Range("f2:g11").Copy Ws.Range("a4")     ':a10") '<~~~ mismatched range sizes
        
        For Each c In Ws.Range("a4:a10")
            If c.Value = Sheets("dates").Range("I2") Then
                c.EntireRow.Hidden = True
            Else
                c.EntireRow.Hidden = False
            End If
        Next
    End If
Next i

End Sub

Hope that helps