Automatic variable generation from data table
Use array, this will reduce by a lot your number of variables.
Name your variable properly ("ten" should be "tenant")
Normaly, variable starts with a lower case in .net
Do not concatenate your strings for queries, this will increase your chances of injections
Your datatable is a bit useless in your case, you can write directly to your variables with a datareader
Your listReport is only needed at the end, I think you could initialize it there instead
I would separate this into multiple functions. A "GetTenants" that returns the list, a "GetTenantID" and a "ShowReport". This way these function can be out of the UI and reused if needed.
Your report takes multiple tenant names but only one ID, this seems strange.

If cmbReports.Text = "Conditions Of Tenancy" Then

    Dim tenants As New List(Of String)
    Dim tenantID As Integer

    Dim propertyId As Integer
    Dim leaseId As Integer

    If Not Int32.TryParse(lblPropertyIDValue.Text, propertyId) Then
        ' Not an integer, this is an error
    End If

    If Not Int32.TryParse(lblLeaseIDValue.Text, leaseId) Then
        ' Not an integer, this is an error
    End If

    tenants = GetTenants(propertyId, leaseId)
    tenantID = GetTenantID(propertyId, leaseId)

    ShowReport(tenants, tenantID, propertyId, leaseId)

End If

Function GetTenants(ByVal propertyId As Integer, ByVal leaseId As Integer) As List(Of String)

    Dim tenants As New List(Of String)

    Using cnn As New SqlConnection(My.Settings.BMSSouthSideConnectionString)
        cnn.Open()

        Dim command As New SqlCommand("Select  TenantForename + ' ' + TenantSurname as FullName From Tenants Where LeaseID = @LeaseID and PropertyID = @PropertyID", cnn)

        command.Parameters.Add("@LeaseID", SqlDbType.Int).Value = leaseId
        command.Parameters.Add("@PropertyID", SqlDbType.Int).Value = propertyId

        Using reader As command.ExecuteReader()
            Do While reader.Read()
                tenants.Add(reader.GetString("FullName"))
            Loop
        End Using

        cnn.Close()
    End Using

    Return tenants
End Function

Function GetTenantID(ByVal propertyId As Integer, ByVal leaseId As Integer) As Integer

    Dim tenantID As Integer

    Using cnn As New SqlConnection(My.Settings.BMSSouthSideConnectionString)
        cnn.Open()

        Dim command As New SqlCommand("Select Top 1 TenantID From Tenants Where LeaseID = @LeaseID and PropertyID = @PropertyID", cnn)

        command.Parameters.Add("@LeaseID", SqlDbType.Int).Value = leaseId
        command.Parameters.Add("@PropertyID", SqlDbType.Int).Value = propertyId

        Using reader As command.ExecuteReader()
            If reader.Read() Then
                tenantID = reader.GetInt32("TenantID")
            End If
        End Using

        cnn.Close()
    End Using

    Return tenantID
End Function

Sub ShowReport(ByVal tenants As List(Of String), ByVal tenantID As Integer, ByVal propertyId As Integer, ByVal leaseId As Integer)

    Dim listReport = New FastReport.Report

    listReport.Load("C:\Users\richard\Documents\BMSSouthSide\BMSPanda\Reports\CONDITIONSOFTENANCY.frx")
    listReport.SetParameterValue("CRMConnectionString", "Data .....

    Dim tenantList As String = String.Join(" ", tenants.ToArray())

    ListReport.SetParameterValue("PropertyID", propertyId)
    ListReport.SetParameterValue("LeaseID", tenantID)
    ListReport.SetParameterValue("TenantID", tenantID)
    ListReport.SetParameterValue("TenantList", tenantList)
    ListReport.Show()

End Sub