Splitting Sandhi

While breaking down "sajjan" (a good person), Mayank thinks the vowel-sandhi rules from last year will apply here too, and gets stuck because both joining parts seem to hinge on consonants. His sister says this is a different kind of sandhi. Who is on the right track?

Breaking down "suresh", Om thinks its two parts "sur" and "eesh" will combine into a matching vowel (like "i+i=ee"). His sister says two different vowels here combine into a third, new vowel. Who is right?

Breaking down "manohar" (charming), Prisha thinks it must be consonant sandhi too, since the last example ("sajjan") also joined two consonants. Her brother says a third thing is involved here — visarga (ः). Who is right?

Breaking down "atyadhik" (excessive), Zoya thinks its two parts are "ati" and "adhik", and assumes two vowels here will combine into a third vowel, like "Suresh". Her friend says a vowel here turns into a consonant itself. Who is right?