Is dual passport allow for my bb?

Dear sirs,
Good day to you all.  I have a situation with this matter regarding my bb passport.

I am a Malaysian, and my husband is Singaporean.  My baby was born in Malaysia, and automatically he follows me that he is Malaysian.  My husband would like the bb to get Singaporean citizenship too so that he is able to stay in Singapore for a long term basis.  Therefore he needs to use Singapore passport to travel. 

Questions arise:
1.  I understand that bb can have 2 citizenship and the children needs to choose the citizenship before 21 years old.  Here, I would like to know since bb has 2 citizenship, could he gets the dual passports? Since my bb is Malaysian , could I apply her a Malaysia passport for him to travel in and out of Malaysia?  So that, when he enters malaysia, he could be able to stay in Malaysia for long term basis which is more than 1 month. 
2.  If my bb is holding Singapore passport, no malaysia passport, when enters malaysia, he is only able to stay in Malaysia for 1 month.  Since he is Malaysian and Singaporean, how can I apply bb to get long term visa to stay in Malaysia? 
3.  Do you know what is the fine charges or penalty for bb overstay in Malaysia if he is using Singapore passport to enter Malaysia? 
4.  What is the penalty for having dual passport before 21 years old?