Hi Jutamind,
When you opt to invest in unit trust, I would expect that you need a professional team to manage your money so that you won't need to actively monitor your investment. That's the main difference of buying unit trust funds vs. directly invest in the stock market.
About your questions:
1. Should we rebalance the portfolio, i.e. buy more of the unit trust which has more losses?
Rebalance should be done. Rebalancing is more like selling some winning funds to lock the gain, or switch a portion of the winning fund to the losing one, just to make the portfolio balance. In your case, rebalancing should be done because a loss of 15% should have triggered a rebalancing act.
2. Or should we set a cut loss % for each of the fund in the portfolio and execute the cut loss strategy whenever the fund hits the loss limit?
Since unit trust fund is a very diversified investment, I think cut-loss strategy doesn't apply here. Unless the fund managers really sucks! If the fund is making a loss due to market sentiment, it is just a great opportunity to invest more to average down or rebalance the portfolio. Unit trust funds unlike some company stocks, it won't result in losing all your investment capital.
3. Or should we cut loss for the losers and hold cash until the loss stabilizes/until rebalance time?
This is about the timing issue. We will never get the timing perfect every time. Constantly rebalance when there is significant win/lose, or whenever your porfolio is unbalance of certain percentage (say 10%) is the most passive strategy that works every time. If you want to invest in unit trust, I suggest that you forget about "timing" issue. Don't predict the market - will it goes up? or further down? If you are going to worry about that, there is no point to invest in unit trust at all.
Just my opinion.
Welcome to the forum!