Well the short answer is No, this is not nearly enough.
Long distance rides are a test of your bodies efficiency as a pedalling engine.
This comes in terms of developing mechanical efficiency, muscular endurance and aerobic endurance.
Spin sessions are fine for a general workout, but they don't replace getting out on your actual bike.
For rides of this distance, there really is no substitute for getting out and spending time in the saddle. You need a good steady diet of 3hr+ rides at least once a week to build up to this.
Most training plans advocate increasing the weekly long ride by no more than 10% per week, so you might build up something like:
Once you reach 130km, then you should in theory be ready for 200km, as at this stage its all about keeping the body fuelled - if you keep eating correctly you can keep pedalling too.
Don't forget to include sufficient rest in your training, as coming into your target ride already fatigued will increase your chances of failure. Generally in the last 5-10 days before you should be reducing both intensity and volume.
Different coaches advocate different patterns of work/rest, and in large part it is down the feedback from the athlete on how well they are recovering. If you are in a hurry to increase your volume for your events i'd suggest starting with a 16 days on, 5 days off program and seeing how you go. By starting on a Saturday this allows you to sacrifice a weekend long ride.
In addition to training, there are other factors you should consider when planning a ride of this length.
The first being nutrition, which you need to practice at - see RoKa's answer for good detail here.
The second is acclimatising to spending such a long time in your cycling position on your actual road bike. You can easily get sore from sitting in the saddle for so long, hands can get numb, lower back can ache, shoulders/neck can get tight and feet can swell or cramp. You simply wont find these things out unless you practice, and you don't want to find out about them for the first time 150km into a 300km ride