You can create a compute field in invoice which will display the highest priority from the line.

highest_seq = fields.Integer(compute='_compute_highest_seq')

def _compute_highest_seq(self):
    for inv in self:
        inv.highest_seq = min([line.product_id.sequence for line in inv.invoice_line_ids])

Now, add this field in Invoice tree view so that you can see which invoice has highest priority of product.