To mine two chains you need double the power, so in this scenario the 51% would actually be 25.5% and 25.5%.
Don't you mean 102%?
No, you have it backwards. To mine 2 chains you need to split your effort between the two chains, so you got 25.5% for each chain. I said it's double the power because the total power is double the power for each chain.
Just think about it. If you have 51% of the total power, how are you planning to get 102%? It's mathematically impossible.