I believe Hayeser has outlined the best option above. It's cool that the mics you've got both have built-in USB, but if you want to use them both at the same time that way, you're likely to run into complications like long latencies and system instabilities- particularly if your laptop is running Windows. There are ways to make it work (for free, which is worth noting if your budget is really tight on this), but you may end up spending quite a lot of time and accruing some headaches doing it. I'll link up a few examples if that option interests you.
The other option, as Hayeser said, is to get a two-input audio interface (which is not quite the same as a mixer) and use your mics' XLR jacks (with a couple of matching cables) to connect them to it. This means the interface can look after all the timing and buffering and such. It's definitely machines' work. And almost all interfaces will allow you to adjust the volume of each mic independently so you can balance the two voices. There are mixers with USB that will also do this job, but in my experience, the USB interfaces on tiny little mixers like these is often pretty shoddy, so buy at your own risk.