Answer:
1. Patty is shorter than her brother.
2. The Dela Cruz family is richer than the Santos family.
3. My room is cleaner than hers.
4. His cellphone is the most expensive of them all.
5. The sea is calm.
Step-by-step explanation:
Sentences 1, 2, and 3 are using the comparative degree of superiority. That means something or someone is more (quality) than something or someone else. In general, if the quality is expressed by a short adjective, we add -er to it (shorter, richer). If the adjective is long, we use "more" before it (more intelligent).
Sentence 4 is using the superlative degree (-est, or "the most/least"). In this case, even though there is still a comparison being made, the person or thing we are talking about is the most or the least (quality). Therefore, we are comparing someone or something to a whole group. Example: Ellen is the smartest of her class.
Sentence 5 is not comparing the sea to anything else. For that reason, it would sound strange to use the comparative or the superlative in it.