Depending on your knowledge/skills/attitude an alternative would be to buy a second hand MTB in CDMX and ride that.
There is no shortage of second hand bikes that would make decent touring bikes available from small shops and the equivalent of pawn shops. I'm thinking especially of old school 26 inch MTBs.
It would take a bit of time to source the bikes but an interesting way to see the city. Most neighbourhoods have several bike repair shops if you wanted to have them checked over or serviced.
Just be aware that when I looked (May 2021) components like cassettes were rare. Findable, but rare.
You don't say about how you plan to carry your gear or if you have some. If a traditional panniers setup I'd suggest bringing your own racks and panniers to fix to the bikes. You may also want to consider bringing suitable tyres as a lot of what I saw available was relatively poor quality Chinese. Of course, that may limit your bike choice in terms of wheel size.
You may also want to consider bringing your own saddle.
Decathlon do have a couple of stores in CDMX that may be useful.
You say nothing about your trip home but buying cheap bikes leaves you relatively free on the other end. I'm sure a local charity would be delighted with two bikes.
If you're lucky you can get to do a shakedown ride on a Sunday in the city when a lot of roads are made car free and the city (and their dogs!) come out to play on bikes, rollerblades and their feet. It's a wonderful atmosphere!
I hate to be that guy but the security situation in México is always something to be aware of. I spent 18 months there and never had a problem but the pandemic has led to various criminal expansion into areas that previously were safe. Do a bit of research and talk to the locals.