How to group multiple functions for parallel execution with Celery?

Question

I wanted to group multiple functions for parallel execution in Django within the transaction.on_commit function -however, I got TypeError: cannot unpack non-iterable int object I have tried to resolve this, but I now think I'm misusing one of the args. This was my initial approach:

# tasks.py

def func_a(keys: tuple, link_set: dict):
    # keys contain random integers as pk
    return 


def func_b(keys: tuple, link_set: dict):
    return 


def func_c(keys: tuple, link_set: dict):
    return 

I tried to call these in my signal like this:

@receiver(post_save, sender=Foo)
def start_task(sender, instance, created, **kwargs):
    if created:
        ...

        keys = (instance.pk, foo.pk)
        link_set = {}
        transaction.on_commit(lambda: group([
            tasks.func_a.si(keys, link_set),
            tasks.func_b.si(keys, link_set),
            tasks.func_c.si(keys, link_set)
        ]).delay())

The 3 functions in tasks.py are independent of each other with no return value, putting them together into one incurs a little cost that I'd like to avoid- how best can I compose these functions for a faster response? Thanks