I don't think you can use ReportItems (e.g. your textboxes) in an indicator expression.

You should be able to use your expressions directly depending on their scope. If they are for each row I'd create calculated fields for them and use these.

If they are summaries for groups then you can use the summary expressions directly in the indicator expression.

As before indicators work on percentage/numeric values so you logic needs to return a value of this type.