Hi Amber...I definitely recommend that you NOT try to keep these 2 species together!!
In the wild, these 2 types of animals would see each other as competitors for food, territory and the like. I would expect a lot of bloody fights, and even fatalities.
It would be best for you to consider either getting another cage for the gerbils (they like to burrow a lot, so a glass tank would be the cleanest set up), or decline to take these new animals in.
Thank you for being concerned about this in advance!
Your concern has touched me--if you have follow-up questions, or need to clarify your case, please let me know right away! Your "Accept" helps me reach out to others!