#models.py
class Company(models.Model):
    name=models.CharField(max_length=50)

class User(models.Model):
    name=models.CharField(max_length=50)
    company=models.ForeignKey('Company', on_delete=models.CASCADE)

class Room(models.Model):
    name=models.CharField(max_length=50)
    company=models.ForeignKey('Company', on_delete=models.CASCADE)

class Device(models.Model):
    company=models.ForeignKey('Company', on_delete=models.CASCADE)
    user=models.ForeignKey('User', on_delete=models.CASCADE,  blank=True, null=True)
     room=models.ForeignKey('Room', on_delete=models.CASCADE,  blank=True, null=True)

#admin.py
class DevicesInline(admin.TabularInline):
    model = Device
    extra = 0
    def formfield_for_foreignkey(self, db_field, request=None, **kwargs):
        if db_field == "Company":
            kwargs['queryset'] = ## Here I don't know ##
        return super().formfield_for_foreignkey(db_field, request, **kwargs)

class UserAdmin(admin.ModelAdmin):
    inlines = [DeviceInline]