Yah I think your underripe, those are usually quite bitter. How long were they on the tree?
"Also, what happens if a lemon tree pollinates an orange tree?"
I'm fairly sure that can't happen. You could have a different orange variety from a similar species pollinate your oranges, but in all likelihood - unless you have a lemon tree flowering at the same time right next to it - and some bees to do the work - it's self-pollinating.