Kinda-sorta. Not many bikes are rated for two adults, so handling and braking will be poor. There's also a good chance of damaging your wheels and tires due to the overload. But if you're riding fairly slow, somewhere with little traffic and preferably fairly flat it can be OK. Some places have weight limit for the passenger.
There are a lot of websites which offer safe bike riding tips. The best one to visit is Bicycle Safe at www.bicyclesafe.com.
no car cood crash
Depends on exactly where you're riding, how you're riding and when you're riding. There are times and places which are just as safe as anywhere else, and other times and places which are outright scary.
Um, probably not. Is it safe to go hunting dressed as a bear?
Yes, because you don't inherit the skill of riding a bicycle.
you will be riding a bicycle
I am not riding
A bicycle
That's all down to how hard you're riding. Most people will use more effort when riding IRL than riding stationary bikes.
poop
A bicycle helmet is a piece of protective headgear intended to be worn while riding a bicycle.
diamondback is a good bicycle for cruising, but not for extreme riding or jumping