Pardon me if some words I use dont sound nice to yr ears.
In traditional thinking, when a woman great preg before married is loose. She will be at a losing end cos she did something that shld be done after marriage thus lost all the bargaining power cos not that valuable.
If yr bf is the only male in the house .... yr scenario is different cos you r giving a heir/grandchild.
If yr bf is somebody who stands by you (fight for you and admit he ought to protect his future wife) then yr future father in law and sister In law cant crawl on yr head cos his words got POWER!
If yr bf is financial unstable means relying on others then half battle gone cos he/you got to see ppl's face, decide yr 'fate' based on others mood.
If you have a house of yr own, you have a better standing ground so not at others mercy.
Getting married at 5wks is possible, no need wait for birth. you dont mind getting married with a ball so y shld others bother/stop you. My uncle (4yrs older then me only) got married when his wife 3mth preg. My grandma so happy cos finally the 36yrs son got ppl want (never had gf before) + got such good 'reward' buy 1 get 1 free !!
My aunt (few mths older then me only), still no news of steady. If she shot gun marriage think my passed away grandma would be very happy to get down n share the joy.
Find out what yr bf plan to do? He planned to let you fight alone or stand by you? Can you apply for HDB flat instead of living with father in law/sister In law (sounds hard to get along) .... give them the pressure that you dont have to stay with them cos you got much much better option. Tell them you just ROM and dont have wedding dinner (if bf is only son) c how 'happy' yr father in law will be .... doubt he want to lose this kind of face.