Hi Riccardo,
Greetings from Syncfusion.
Query 1 - to make the Dependency tab of the edit dialog uneditable
For this query, we suggest you set the allowEditing propety 'false' in the predecessor column field. Refer code snippet for more information.
Code-Snippet: -
columns: [ { field: 'Predecessor', allowEditing: false }, ], |
Query 2 - to resize the columns of the same tab? (the Id column is way too small to show the IDs I'm using)
To resize the ID column in the dependency tab, we suggest to use actionBegin event to achieve your requirement. Inside the event, you can modify the column's width. Refer the code snippet for more information.
Code-Snippet:
actionBegin(args) { if ( args.requestType == 'beforeOpenEditDialog' || args.requestType == 'beforeOpenAddDialog' ) { args.Dependency.columns[0].width = '200px'; } }, |
Cumulative Sample - Scmddx (forked) - StackBlitz

Regards,
Sridharan