Hello Lorly168,
Going by your statements, looks like you do have very stable employees--else this situation wouldn't have arisen.
And, I don't think there's anything to feel bad about introducing a short-sighted policy AS LONG AS you are willing to learn & correct ALONG THE WAY. There are many companies who fail in this crucial aspect.
Coming to your query/concern, pl confirm the domain/sector your company is into--IT, Telecom, etc.
And since you are in Philippines, suggest evaluate the general Leave Policies in other similar-sized companies in the same sector. This would give you some semblance of being on-par with Industry standards & ensure your employees DON'T resist whatever changes you bring about.
As far as 'how to fix the situation', suggest FIRST consolidate the pending leave dues of each employee into a Fixed leave balance rounding-off to the nearest numeral--AS ON DATE. You could retain the Leave balance as it is or maybe pay the employees a Fixed amount for the leaves you wish to be 'abdicated/lapsed'.
THEN INTRODUCE the new Leave policy which will get into effect from a pre-determined date, which obviously you need to inform the employees in-advance.
With some fine-tuning, you should be able to get a model that will be, by & large, acceptable to all--and more importantly, that would stand from the 'long-term standard' viewpoint.
All the Best.
Rgds,
TS