SKP1) In the patterns:
a) Subject + verb + someone + something
b) Subject + verb + something + to/for + somenone
is something always the direct object and someone always the indirect object?
c) Carol wrote her boyfriend a letter.
her boyfriend -> indirect object
a letter -> direct object
Is this correct ?
Yes, it is correct. With verbs that can be followed by two objects, the indirect object typically comes immediately after the verb, a similar example:
The doctor sent me a bill for his services.
Here bill = direct object; me = indirect object
2) Are there other names used in English grammar for
direct object and indirect object?
These are the usual names but some say 1st object and 2nd object
3) Only the prepositions to and for appear in constructions as the pattern above or are there other ones?
A prepositional object usually replaces an indirect object as:
Serve the old lady dinner.
"Serve dinner to the old lady."
Actually, it can be discovered by asking TO WHOM or FOR WHOM after the verb: So "to' and 'for are the two prepositions used.
Thanks in advance
P.S.: Feel free to point our any possible mistakes on this post.