you are getting mastered Thai, as you can noticed those questions. let me explain lil about it. *ภรรยา (why it's pA rA) whenever you see double รร ,can read 2 way: 1) after รร have no consenonts/ read as "an" vowel ex: บรรทม read as /ban-tom/ กรรไกร read as /gan-glai 2)after รร there are consenonts/ read as "a" vowel ex: วรรค ค is its ending consenont, read as /wak/ สรรพคุณ พ is its ending consenont, read as /sap-pa-khun/ สุวรรณ ณ is its ending consenont, read as /su-wan/ ex: สุพรรณ วรรณะ วรรณยุกต์ สุพรรณี คน or ผม (O) most of them just 2 consenonts will read as if "O" vowel appeared. yes, for this Peachey is mentioned it. สวัสคี (sA) most of thai word, the vowels omited in the syllable or consenont, those word you need to memorise them, they are word the root to sanskrit word. but most of the case read as if it have "a" ex: สวัสดี สบาย สดวกสบาย ฉลาด เฉลิม ขนม ...............................so on , those are read as "a" goodluck for your study, Priviat and sposiba

Each Thai syllable has a natural vowel called อ อ่าง (or more correctly, อ อ่าง doesn't have a consonant sound), so this would be the A/O sound you hear. If you want other sounds like I, U, E, tone adjustment, or even a shorter/longer vowel, then you add the appropriate marks.