> I am a college student graduating in June, and I was fortunate enough
> to sign a new grad software engineering full-time offer back in
> September with a medium-sized startup.

"fortunate" is not what I would call it. Now that the company is being acquired, that offer is not worth the paper it was written on. You need an actual written contract, not an offer. And considering the purchase, you'll want a carefully crafted contract because even a contract can easily be reneged on. 

For now, restart your job search. You must proceed with your job search as if you don't have a job secured yet (because you really don't and you never actually did).

Then, talk to them. Tell them your concerns. If they make you any assurance, ask that those assurances be included in your contract. Those employees wanting to hire you could promise you the moon, but it doesn't really matter what they promise. Next month, they could all be replaced or moved to a new role or some could even have moved to the Bahamas with all the money they've made on the stock sold to the new company. 

And finally, do some research on the acquiring company. What are they known for? What have they done in the past? Why are they buying it? To expand their capabilities and market share, or to cut costs, kill off the competition, and consolidate?