1. "Whose loud and shrill cry is this?" sounds most natural to me. 2. "meddle in other people's" or "meddling in other people's" would both be OK. Use "in" not "into." 3. "What I like to do most is [to] eat" -- because you use "do" it is better to use "eat" not "eating." Or, you could write "What I like doing most is eating." Do == eat; doing == eating. Sounds best that way. But the next sentence is different. "Two things I like to do are (not "is") reading and hiking" -- because the sentence focuses on "things," it makes sense to use the gerund nouns "reading" and "hiking".

1. "Whose loud and shrill cry is this?" would be correct. "so loud" would not work in this sentence. The word "loud" already means making a lot of noise, so you do not need it. If you really want to use something, you can say "Whose very loud and shrill cry is this?" 2. For the second one, that sentence is perfect. It would be meddle. If you wanted to use "meddling" you would say, "stop meddling into other people's lives" 3. "What I like to do most is to eat" would be grammatically correct. Then "Two things I like to do most is to read and to hike" or you can also say "Two things I like to do most is to read and to go hiking"