Moving

The decision is hard to advise on without knowing if further building on the land below you could take place after the four houses are built, in which case would advise to move now whilst there are just four houses.
And if there isn’t access from your road and you have a sea view I think you still have plenty to recommend your property. Two years is a long time as we get older and once your house goes up for sale the whole process could take some time. Would get some valuations from estate agents done and ask their advice.

Why not sell now?

At your ages, live your life right now. Don't hang around waiting for the future to happen. In case it doesn't.

Any serious contender to buy, will go over the planning consent in detail and realise it's no threat to your property, its access, sea view etc. Good way to weed out any timewasters.

You can only test the water by putting it on the market. On the coast, summer is often a good time to sell, especially with a sea view. Unlike town properties, when it’s hot and holiday time.
As has been said, any planning for future development will be flagged up by the searches, if not before.

I would be selling now too.

I know someone who sold.
Not quite the same circumstances as you, but close.
Dont think they took a financial hit at all.
But the housing market was a little more bouyant than it is currently[in England].

Sell now OP before the mess starts, they will see planning permission and you will take a hit but so be it, sell while you are two and able to work together, to make a new home comfortable