No easy answer. There are many different sealants, but generally two types: resin and glass-ionomer cement. However, each of these types can have many different formulations. For example, resin dental sealants can be clear, white or green, filled or unfilled, have fluoride. They can be hardened with a light, or over time. Contact manufacturers for specific content and percentages.
Depends on brand. The best way to find this information is to go the the website of the company of the sealants brand you are interested in and download the msds sheet for the product. If you are concerned about bpa, ultradent makes dental sealants that are bpa free.