It depends. You may have two bikes on the same Peloton subscription, but they can not be ridden, or logged into, at the same time.
If you have two houses, a bike at each house, and there will never be overlap of people riding them, both bikes may share the same Peloton subscription.
If you have two bikes, either at the same house or at two houses but people may be on both at the same time, each bike will require its own subscription.
Note that the official response from Peloton support is that you will need two subscriptions. However, here is the workaround. When you purchase your second bike, your account gets loaded with a second “empty” subscription (which does not start billing you until a bike is activated to it).
When you activate your second bike, you are presented with a screen where you have to choose which subscription to tie the new bike to. You’ll see 2 subscriptions listed. One for your old bike, which will show “In Use”. And a second, new subscription, that shows available. The usual/normal/official method to activate the new bike would be to pick the second available/empty subscription – at which point you would have two active subscriptions, be billed twice, and be able to ride both bikes at the same time.
However, if you instead pick the subscription that is tied to your old bike, your new bike will claim that subscription. Your old bike will then be deactivated. You now are using your new bike, with your old subscription, so are only paying for one subscription. However, at this point, your old bike has no subscription, so if you turn it on, it loads the activation screen. You can repeat the same process to get your old bike back on the same subscription, but when you do that, the new bike then is inactive. This process can be repeated back and forth as you move between your two bikes, but it is impossible for both bikes to be ridden at the same time with this method.