actually there is not any diferent types oy pronouciation.

there are two types of languages in sinhala one of them is speaking language the otherone is written language just like formal and informal in english.

according to written language the words mentioned in the above has become,

mama liyami

mama kami

mama bomi

mama andami

but in speaking language,

mama kanawa

mama bonawa

mama andanawa

mama liyanawa

there is a difference between singular and plural when you use sinhala as a written language

sigular noun           plural noun

man                       people

i                            we

you                        you

miniha,minissu/mama,api/numba,numbala.

miniha liyami /minissu liyathi

mama liyami/api liyamu

numba liyai/numbala liyathi

but in speaking language we tell any verb without a diference between in singular plural for any subject like liyanawa kanawa bonawa andanawa

va is used with present and past tense verbs in sinhala but in future tense it has become vi.for example,i wrote a letter(liv'va'),i write a letter(liyana'va'),i will write a letter(liya'vi') in addition va is used in sevaral nouns like mother(ma'va'),year('va'sara=varshaya),rain('va'rshava,vassa)

i can give a correct answer if i am able to listen 'va'

I'm not sure how exactly explain it in English. Lets see.

When we pronounce ලියනවා (writing) in Sinhala, the වා is said for a little longer time than the ව which is used in වයස (age). The difference is the time we keep saying it. When I write it in English, I used to write each kind of word using 'wa' but the above difference is there.

Does it help?

I wish I can explain to more exactly. May be you can learn the correct pronountion by litenning to someone speaking such a variety of words. Then you can get it correctly I guess.

In reply to Asanka: I get confused when words like 'liyanawa' are written with a 'ව' which makes me think it should be 'liyanava' which I have seen it sometimes spelt like. Liyanawa is just an example, so therefore: How would you pronounce ලියනවා? Are there different ways to pronounce 'va' for different type of words?: I have been told  'ව' can be pronounced either 'wa', 'va', or 'vwa'...? I hope that this has made more sense.