Yes, you can use your CPF-OA to finance for your second property, provided you have set aside the "half minimum sum" in your CPF-OA/SA accounts.
For loan, it will be assessed based on your age and income, subjected to TDSR, along with your current of outstanding mortgage loan. If your HDB is fully paid, you may be able to loan up to max 75% of the new purchase. If your HDB is still under loan, max loan would be 45% for second property.
Should you need any further assistance in matters relating to property, please contact me at my mobile 9748 6305. I will be happy to assess and share with you the possibilities for you and your partner in the current market.