Civilization 5 – Does an Embargo Stop Trade Routes with Team Mates?

The diplomacy summary that you get from clicking the scroll in the upper right will show you all the civs and city states at once, as well as what resources they have available, how much gold they have, and how much gold per turn they are making.

It is not possible to disable science sharing.

The game does scale the science requirements of technologies when teamed up, so that a team of 2 needs to generate 150% science to be at the same advance rate of a single player as evidenced by looking at the tech tree in each case:

Team Size | Agriculture | Pottery |Sailing | Future Tech 1 | Scaling
----------|-------------|---------|--------|---------------|--------
1         | 14          | 25      | 40     | 7001          | 100%
2         | 21          | 37      | 60     | 10501         | 150%

Obviously this scaling is somewhat below what you would expect, and does give something of an advantage. The best workaround for this is to team-up the AI players into pairs so the playing field is more balanced.

Also remember that the AI will receive difficulty bonuses based on the lowest difficulty out of all the human players, which can impact on their science rate.