"We like mangoes."
Translation:हमें आम पसंद हैं।
Hum becomes Humay - ie. The ending changes.
You've seen that that's the same with Tu, Thum etc.
If the ending changed for Peter it would have to become Peteray.
That doesn't happen, instead it gets a post position as Peter Ko.
Humay doesn't need Ko because it's already got -ay.
You have two options for saying "I like something":
मैं कुछ पसंद करता हूँ (I do liking (to) something).
मुझे कुछ पसंद है (To me (from) something liking is).
They may both sound a little cumbersome to English speakers, but this is how it works in Hindi. Same rules go for 'to love'.