My family goes to the United States every year for Christmas. This year the visa B1/B2 expires. Is it possible to renew our visas when we are within the United States, instead of renewing it in the country we applied from?
Note: I am not asking for visa extension.
No. You cannot receive a US visa from inside the United States (there are some exceptions for diplomats and foreign government officials, but those are special cases).
You don't have to apply for a visa in your country of origin (you'd generally apply wherever you are resident), but there may be a higher risk of refusal if you apply away from your home in some cases.
US visas only need to be valid on the date of entry, so you could still use yours for this trip even if the visas will expire during the time you are in the US.
Visas aren't issued inside the US, but on the other hand, the visa expiry date does nothing to your status in the US. Rather, it is by the date stated on the entry stamp in your passport that you must leave.
In fact, you can undertake trips of max 30 days to Canada or Mexico and then re-enter the US, in case you're within the period of stay granted on entry but having an expired visa.
However, for your 2019 visit you'll need to obtain a new visa, which can only be done at a US embassy/consulate.
