1- No, The second marriage is void and the children are not "legitimate".
The law I cited states:
5. (1) Every person who on the appointed date is lawfully married
under any law, religion, custom or usage to one or more spouses
shall be incapable
, during the continuance of such marriage or
marriages, of contracting a valid marriage
under any law, religion,
custom or usage with any other person, whether the first mentioned
marriage or the purported second mentioned marriage is contracted
within Malaysia or outside Malaysia.
6. (1) Every marriage contracted in contravention of section 5
shall be void.
2- Yes he can be prosecuted for bigamy. The law I cited states:
7. (1) Any person lawfully married under any law, religion, custom
or usage who during the continuance of such marriage purports tocontract
a marriage under any law, religion, custom or usage in
contravention of section 5 shall be deemed to commit the offence
of marrying again during the life-time of husband or wife, as the
case may be, within the meaning of section 494 of the Penal Code
3- No, Malaysian law only allows one marriage at a time to be registered by a non-Muslim.
I hope this information is helpful.