Thanks gents. Divorce not an option, otherwise wife can't stay in Switzerland.
To summarize and to do list
Father: German citizen, worked in SG for 5 yrs on Employment pass, have left permanently to CH, no taxes outstanding, no
property etc
Son: Never SG passport/SG local school/SG anything. Holds mandatory CPF account. Used GER passport to travel/emigrate
Son's age Son (SG / German dual citizen by birth)
0.0 Born in SG to SG mother, GER father
4.8 Left SG for Switzerland (CH); notified ICA of address change
4.8 Got temporary CH residence permit
8.0 Today, email ICA about intention renounce citizenship, get their answer that not possible til 21
9.8 Get permanent Swiss (CH) residence permit
11.0 Notify ICA and CMPB of intention to defer and renounce (earlier due to slow processes due to Covid)
13.0 Apply for deferment pending renunciation at age 21; SG mother sends documentation that she has CH permanent residence and that earliest date for her CH citizenship is when son is nearly 15; son sends SG birth cert, German passport copy and German birth cert, Letter from Swiss school confirming attendance, proof of departure from SG
13.0 Apply Exit Permit 1 yr 364 days (online, no bond), Reason: emigration. Not needed if deferment approved. What if approval process takes longer? Assume apply for exit permit (reason: emigration) for 1 yr 364 days
14.995 Re-Apply Exit Permit 1 yr 364 days (in Singapore in person? Online? No bond?) Reason: emigration
16.5 Register, no need for medical checkup if deferment is approved
21.0 Renounce SG citizenship, i.e. no chance to ever get employment pass, student pass etc. Just tourist visits
Wife: No HDB, loans, grants, benefits, MOE stuff. Short visits to family (less 1 month per year). Holds mandatory CPF account
Son's age Wife (SG citizen)
4.8 Left SG for Switzerland (CH); notified ICA of address change
4.8 Got temporary CH residence permit
9.8 Get permanent CH residence permit
14.8 Apply CH citizenship (earliest possible date), takes up to 2 yrs to get the citzenship
16.8 Get CH citizenship latest (2 yrs process) and then proceed to renounce SG citizenship
As an aside: Son could apply CH citizenship age 11.5, and possibly get CH citizenship by age 13.5. But then he would have to do Swiss NS
Also know of Singaporeans in CH- their kids did Swiss NS and SG still wants them to do SG NS as well...
MS, if you're still alive by then (as you wrote it), and I hope you have a very long and healthy life, how would I be able to contact you. Should I PM you my email address?