class Product(Model):
    name = CharField(...)
class Contragent(Model):
    name = CharField(...)
    addres = CharField(...)
    phone = CharField(...)
class ConrtagentPerson(Model):
    name = CharField(...)
    second_name = CharField(...)
    phone = CharField(...)
    email = EmailField(...)
    company = ForeignKey(Contragent)
class Order(Model):
    product = ForeignKey(Product)
    person = ManyToManyField(ConrtagentPerson)
.......
name=request.GET['name']
person = ContragentPerson.objects.get(name=name)
all_person_orders = Order.objects.filter(person=person)