public class Ticket
{
    public int Id { get; set; }
    public int ScheduleId { get; set; }
    public int SeatId { get; set; }

    [DataType(DataType.Date)]
    [Column(TypeName = "Date")]
    [DisplayFormat(DataFormatString = "{0:yyyy-MM-dd}", ApplyFormatInEditMode = true)]
    public DateTime ForDate { get; set; }

    public Seat Seat { get; set; }
    public Schedule Schedule { get; set; }
    public ICollection<TicketStop> TicketStops { get; set; }
}

public class TicketStop
{
    public int Id { get; set; }
    public int TicketId { get; set; }
    public int LineStopStationId { get; set; }

    public Ticket Ticket { get; set; }
    public LineStopStation LineStopStation { get; set; }
}

public class LineStopStation
{
    public int Id { get; set; }
    public int LineId { get; set; }
    public int StopId { get; set; }
    public int Order { get; set; }
    public bool IsLastStop { get; set; }

    public Line Line { get; set; }
    public Stop Stop { get; set; }
}

int startStationOrder = _context.LineStopStations
            .First(l => l.LineId == lineId && l.StopId == startId).Order;

        int endStationOrder = _context.LineStopStations
            .First(l => l.LineId == lineId && l.StopId == endId).Order;

public List<Seat> GetAvailableSeats(int lineId, int scheduleId, int startId, int endId, DateTime forDate)
 {
   int startStationOrder = _context.LineStopStations
       .First(l => l.LineId == lineId && l.StopId == startId).Order;

   int endStationOrder = _context.LineStopStations
       .First(l => l.LineId == lineId && l.StopId == endId).Order;

   var reservedSeats = _context.TicketStops
       .Where(t => t.Ticket.ScheduleId == scheduleId)
       .Where(t => t.Ticket.ForDate == forDate)
       //basically I don't know how to proceed here.
       //In pseudo code it should be something like:
       .Where(t => t.Min(Order) >= endStationOrder || t.Max(Order) <= startStationOrder

 }