The translation of this sentence is the biggest mystery in the internet. Though you can get an easy answer by just translating it directly to English, it is doesn't sound right. But when using conversational, you can get it right. So, here are some of the cleaner answer for "Pang ilan ka sa magkakapatid in English".
What is your birth order among your siblings
Q: How many siblings do you have?
A: 2 brothers and 1 sisters
Q: So where do you fit in that order?
A: I'm the eldest.