The usual 一起 grammar structure is
Subj. + 一起 + Verb + Obj.
Expressing "together" with "yiqi"
Adding 要 after 一起 interferes with this structure: it's possible to misinterpret 要 as the verb.
Comparison
There's actually three places 要 (which has a few meanings) can be added:
-
今天晚上老板要和我们一起加班。
Tonight, [the] boss [wants to/needs to/is going to] work overtime together with us.
So we have:
- the subject is 老板 = "[the] boss",
- the verb is 要, and
- and what they want to do is 和我们一起加班 = "to work overtime together with us".
This seems unproblematic, and probably the most natural.
-
今天晚上老板和我们要一起加班。
Tonight, [the] boss and us [want to/need to/are going to] work overtime together.
So we have:
- the subject is 老板和我们 = "[the] boss and us",
- the verb is 要 = "want to", and
- and what they want to do is 一起加班 = "to work overtime together".
This also seems unproblematic.
-
今天晚上老板和我们一起要加班。
Tonight, [the] boss and us together [want to/need to/are going to] work overtime.
This one is more complicated:
- the subject is 老板和我们 = "[the] boss and us",
- the verb is 一起要 = "together want to" or "together need to" or "together [are] going to" (??), and
- and what they together [want to/need to/are going to] do is 加班 = "to work overtime".
I feel this one is ambiguous because what follows 一起 is 要, so it's possible to interpret 一起 as applying to 要 and not necessarily to 加班. Something in English to indicate the difference:
We don't work at the same company, but we're together wanting to work overtime to save money for an upcoming concert.
But realistically, it's a very contrived interpretation. So I don't believe the Chinese here is wrong, it just sounds a bit weird.
Baidu
Compare the Baidu search results:
(The number 76,000 is likely hugely inaccurate, but there's a lot.)
We consistently see that 一起[2-character verb]
does not want a 要 in between.