Does working overseas affect my application for HDB loans for BTO?

Yes you can apply with your mother. No issues there on family nucleus.

Working overseas does not affect your loan. However the job must come with the correct documentation. Please prepare the following to ensure you can get the loan.

1) 6 months payslips

2) 6 months salary crediting bank statement reflecting the exact same amount as your payslips being credited

3) An employment contract showing you are a permanent hire and not a contract / temp staff

Yes you can, so long as you still hold the SG citizenship. By the way, is your mum still working? If so, she may be the Main applicant and you be the Co-applicant.

If you're applying with you mum, I don't think you'll need to wait till age 35. You can apply with her as the co-applicant.

Perhaps you can try to apply the HLE to see if they impose any conditions or restrictions.

You'll get a better picture.

Hope this helps.