Is there anything I need to ask or consider during my negotiation
process based on the fact that they probably will soon be own by
Very tricky situation.
You are being hired by one company, and one hiring manager. But you already know that there are big changes ahead. What you don't know is how all those changes will actually play out. You will at least end up working for a different company.
I've worked for several companies in the past that were acquired, and some that acquired other companies. After each acquisition, the nature of the company changed significantly. Some teams were let go completely (often "overhead" departments like accounting, marketing, etc, that were handled at the corporate level), some teams were moved to a different location, others stayed the same. Sometimes management changed. In one case I was working for a new boss who worked out of the home office in another state. The time frame for these changes ranged from immediately, to several years after the acquisition. For me at least, some of the things that made the job appealing earlier typically were gone.
Try as best you can to ask questions about the acquisition, and about the nature of the acquiring company. If they are allowed to tell you the name of the company that is acquiring them, do some searching. See if you can find out how the company typically deals with acquisitions - do they immediately let almost everyone go (keeping only the "essential" few), or do they run new acquisitions as separate divisions and leave them alone for at least a while?
Try to find out from your hiring manager what their expectations are for your specific team post-acquisition.
Try to find out if anything within your offer is subject to change, post-acquisition. Are you being hired under the old, pre-acquisition rules? Or under the new, post-acquisition rules?
The fact that you even know the company is being acquired is good. Often, companies cannot even divulge that fact until very near the end. On the other hand your use of the phrase "probably will soon", makes me wonder how much is definite here.
Here's something you might wish to read: https://workplace.stackexchange.com/questions/20357/a-coworker-beat-me-to-resignation-how-can-i-resign-in-a-professional-manner