If I can acquire multiple assets, can I acquire some into my possession and then, during the same acquire assets action, acquire the final card which then acts on those newly gained possessions, for instance enabling me to give any number of Item possessions to another investigator?
I've been unable to find any references for this question.
If you think of the Acquire Assets action as a shopping trip it helps resolve the more common mistakes (replacing items as they are purchased instead of at the end and not being able to purchase more than one item. Shops don't restock immediately after you purchase an item, it takes time to do so; and your successes are each worth one currency, you can divide your total currency as you want)
I believe looking at it this way also resolves your question.
When you're shopping you're not buying items at random, you're selecting the items you want, deciding between multiple items and preferring certain items over other ones.
With that in mind:
You've purchased all your items at the same time. You own them all simultaneously. You can then choose the order to resolve any effects that occur as a result, and if that includes effects that allow exchange of items between players then the new cards are included.
Alternatively, you've purchased the items in individual transactions from multiple shops in the same shopping trip. The items you've purchased already have been paid for and are in your possession. Effects from items you've purchased later will still apply to these items (but not future purchases).
As I said, there are no official answers to this question that I can find, but hopefully this answer gives you some guidance.