Assuming Azure Lighthouse is setup correctly, you should be able to navigate to each Sentinel instance/workspace ok?
Are you talking about Azure Dashboards, if so you can add a new Tile to your Dashboard linked to your customers data. Maybe setup a specific dashboard in your central tenant for this?
Also with Lighthouse when its setup you can use a Workbook (dashboard) to see the customers data, one to start with is "Sentinel Central" in the [Content Hub] which is designed to monitor Incidents across Tenants or multi-workspace.
I did two posts for v2 https://www.linkedin.com/pulse/microsoft-sentinel-central-workbook-v20-clive-watson/?trackingId=YU4sDjiHSWCw4g5pVjMzyQ%3D%3D and there is a link to v1 within.