When is it acceptable to combine expressions of probability with expressions of expectation/planning?

While working on expressions of probability with some ESL students, the question came up of whether it'd be ok to say something such as:

Hopefully, they will probably help us out in the future.

My knee jerk reaction to this sentence is to say that you should pick one or the other, either 'hopefully' or 'probably' but I haven't been able to find a thouroughly well-reasoned explanation as to why that is the case. Some combinations are obviously nonsensical in that one expression clashes with the other, for example:

Hopefully, this will certainly be useful.

Or

We are planning to definitely complete the assignment in time.

There's an inherent sense of uncertainty in 'hopefully' and 'planning to' that doesn't match the adverbs used further down the sentence. However, it wouldn't strike me as odd to see an action framed as a plan or expectation being used together with an adverb that denotes some level of uncertainty, like this:

We are aiming to maybe finish in 2 hours, 3 at the most.

Would this be an exception to the rule or is it simply a matter of the terms used not clashing in the perception of certainty/confidence they create? I'd love to know if there is some kind of formal rule or study that explores this in more detail.

Solution 1:

There's a name for repetition that adds nothing: tautology.

Oxford Lexico example for tautology: It is conceivable that the key to truth lies in tautology and redundancy.

Hopefulness and probability are too close in meaning, like Big Fat Greek Wedding, where the tautology is funny. Other times, you need tautology for emphasis, like "Cash only. No checks."

Also, hopefully, as here, is notorious for not applying where it sits: While you are hopeful that they will help, you say "Hopefully they." So, are they hopeful that they will help?

Solution 2:

It looks like you wonder if you can use two adverbs naturally at the same in a sentence.

You should keep in mind that "adverb" is just an additional information in a sentence(not the core).

Hopefully,

they will probably help us out in the future. (I can't find what's wrong) Hopefully and probably, they will help us out in the future.(Alternative)

Hopefully,

this will certainly be useful. (the same as above)

Hopefully and certainly, they will be useful.(Alternative)

We are planning to

definitely complete the assignment in time. (same)

It's important that the speaker choose the right word which is natural and idiomatic.

This question is: not objective but subjective and not quantitative but qualitative