Do what you've been doing. :)
I believe you use the condo rental income to pay for itself for the one rented out.
So does the HDB.
There should be balance from the HDB rental or some from the condo to help fund the condo you've been staying.
So continue to do so and work part time if you want to or do whatever that makes you felt fulfilling (voluntairy work, teach someone something you know best but they donno, just like Seedly) since your property mechanism are more or less self-funding and you still have CFP retirement $ for retirement.
Thus enjoy life now with what you have, enjoy the time with your love ones and so on :)
Need more info:
Do you have any Cash, or equity that can help lessen your loan?
Any emergency funds?
Are you planning to retire after 55?
Can the rental income cover your expenses plus all mortgage?
Any insurance to cover incidents?
From the Question you posted, it sounds like you are just asking if you should sell 1 of your property. Basically you just need to assess if you can afford it.