Out of court settlement for what? That particular lawyer has misguided you.
1) first of all you need not be scared of any criminal prosecution against you, as you indulged in consensual sex with an adult female.
2) Your wife too cannot prosecute you criminally, as you didn't commit an offence of bigamy.
3) The only thing your wife can do, us seek divorce in family Court. It's a civil matter and doesn't involve punishment. She may seek alimony.
4) That bar girl has no legal right to seek maintenance .
5) Now for the twins... Well yes you will be responsible for their maintenance, but for that, they have to establish that they are your twins, by way of paternity test (DNA test)
6) So the bottom line is, you need not be coerced into going for any settlement with the bar girl.