This scenario is possible and in order to achieve it you should use the NumericTextBoxSetting and the TextBoxSetting features of the input manager. Both have a Validation-IsRequired property which should be set to true. The ID's of the simple text boxes should be specified as target control IDs for the TextBoxSetting and the ID's of the numeric boxes go into the target control IDs of the NumericTextBoxSetting.
I hope this helps.
the Telerik team