Share your design specs only, and let each platform team write the implementation in the language that they think best.
Yes, you'll have two teams spending time on doing the same thing. However, you'll get important benefits.
Each team will be able to implement appropriately for their platform. While iPhones and Android phones are rather similar in terms of capability, the interaction models have a lot of differences, and forcing a common component often results in non-native feeling apps. Users will be at best confused, and at worst insulted by this.
Additionally, when you have two teams working on similar problems, they can help each other. Training on this interaction with things known to be pretty much the same helps people realize they can do it with things that aren't obvious. Meeting on a regular basis to discuss things that worked/didn't on the various platforms will help them all.