EC in 5 years or continue living in HDB? 55YO, no debt, 3 dependent all employed.?

Need more info.

Currently owns 4rm HDB valued at ~400K.

Need to know CPF and accured interested and CPF life. Husband, wife if use to pay HDB.

Opportunity presents itself to rent an EC @ ~$2.5K/mth for 5yrs to help friend fulfil MOP (he is Overseas). Possibility of buying over in 5 yrs.

Note: Holding a depreciating asset and buying a appreciateing asset.

Few options available:

1. Go ahead, sell current flat, buy private to rent out, may buy over unit in 5 years.

Good

2. Go ahead, rent out current flat, either sell HDB unit at end of 5 years (to buy EC or new BTO) or go back to live.

Bad.

Wondering what's the best way to benefit from this situation?