The correct word is are. I understand your confusion, though. There is a number disagreement between subject and predicate.
Using a plural verb in this case might seem to contradict CGEL's section on "Coordination with and" (Ch5 §18.4(a)) which might be misunderstood as saying the phrase a great team can only apply to the subject Amelia and Jessie "as a unit, and hence a plural verb is impossible." The key part of that override though is the subject needs to be conceptualized as a single unit.
In this case, despite the singular team, Amelia and Jessie are not seen as a single unit. They are understood to be separate members that are each part of the collective team. Since they are conceptualized as separate members, the verb should be plural.
More information about overriding subject-verb agreement and collective properties:
Ch5 §18.2 : Semantically motivated overrides with collective and number transparent nouns
The subsection, Complementation, in 18.2 has a list of more collective nouns.
Ch5 §19.1 : No agreement of number
This is particularly relevant to this question.
Ch5 §19.2 : Collective properties
This mainly discusses collective nouns in the subject but might still be helpful.