CoordinateConverter | Convert Coordinates to and from L/L , L/L Decimal

I am Building a rectangular Grid of Homogeneous Buttons with Dynamic Rows and Columns to Be set at Runtime. The Code is in Xamarin. All the latest versions etc. Entire Project can be Downloaded here: https://github.com/BicycleMark/XamSweeper The Problem I am having is the MultiBinding Portion of the XAML. Any review or suggestions would be super-excellent

I used Nested StackPanels to create the Grid like this:

I succeeded at creating a MultiValueConverter for sizing the Buttons which are appearing correctly. I have Tested the Converter with a Unit Test and it functions as Expected. the [R,C] is printed in the Test of each Button. These are pulled from Model which is bound Correctly

The problem I am having is in Linking the MultiBinding to 3 Items I need to calculate Size for the Buttons:

The Width of Each Button is calculated with these three parameters

1. ActualWidth of Frame Holding the Buttons
2. Number of Columns Of Buttons Of Model
3. Spacing or Padding between each Button
4. If any [1..3] are null return 50 <--- This is What I return because my Binding is not working

The Height of Each Button is calculated with these three parameters

1. ActualHeight of Frame Holding the Buttons
2. Number of Rows Of Buttons Of Model
3. Spacing or Padding between each Button
4. If any [1..3] are null return 50 <--- This is What I return because my Binding is not working

Here is the Converter Described: