How do I write a letter to donate my properties to one orphanage after my death?

You don’t do it through a letter at all, my friend.

Bird’s eye view:—

The most efficient way is through a trust (to hold the properties as trust assets) plus a pour-on Last Will — both set up through your lawyer in your living years.

The Last Will lays out the masterplan for your “after affairs.” By law everywhere, Last Wills must go through probate court and the payment of death taxes (estate duty, etc) before distribution to beneficiaries.

But since the properties have been set up and held by a trust, those are trust assets. Trust assets don’t need probating. The Last Will simply becomes an indicator that a trust exists. So at the moment of your demise:—

the trust assets are almost immediately distributed to the beneficiaries (like that orphanage),

and the trust itself will also have prearranged for the title transfer of the properties to the orphanage.

In some countries, death taxes are lower (or even waived) for trust distributions — payable by the trust itself in various ways.

Without a trust, the properties would remain part of your estate for probating. The orphanage might be unable to accept the properties because it has to face paying the death taxes and arrange the bureaucracy of the title transfers.

What happens if you don’t do any of the above?

It gets real messy real quick.

If you allocate anything only through a Last Will, then everything is part of your testate estate.

If you don’t have a Last Will, everything becomes your intestate estate — and even the probate court wants to avoid your case.

So whether testate or intestate, everything has to go through probating, which can easily take up a whole year (or several years) to finalise.

With a Last Will, your Executor would be drowned in a sea of paperwork for distributions, death taxes, property taxes, title transfers, etc.

Without a Last Will, the probate court has to appoint an Administrator (at the expense of your estate) to handle your after affairs.

If your estate contains any quantity of immobile (“real”) property and/or the probating gets overly complex or the assets cannot be distributed properly, your entire estate could end up being taken over by the government instead (via resumption, compulsory acquisition, etc).

The government then sells off your estate for scrap and the proceeds go to the government treasury.