Promissory Note in exchange for Original TCT copy

Hi.  Two sisters borrowed money from me and in exchange gave me the original copy of their property's TCT as collateral and signed a Promissory Note.  The TCT is under the name of their father who is already deceased (and they are the forced heirs together with their mom and siblings).  They have 2 other siblings and mother, all residing in US.  The Promissory Note allows me use of the property and for them to pay interest on the loan.  

After a few months, they negotiated to sell the same property to me on installment basis  and we agreed with the terms and conditions of the sale.  I then decided to build improvements on the property with their consent while waiting for their mom to return to Manila for a vacation and to finalize the sale via a written contract.

When their mom returned to Manila, a Contract to Sell was drawn up this time involving all the siblings and the mom.  However, the terms and conditions stated therein are not what we have originally agreed verbally.  I then decided to not go through with the sale because all the terms and conditions stated in the contract are in their favor.  I then asked the sisters to pay me the following:

1.  Cash owed to me + interests
2.  Expenditures on the property for its improvement all supported by receipts (because I would not have started any construction on the property if the sale has not been agreed by all parties albeit verbally)

Questions:
1.  Can I be compelled to turn over the TCT to the other heirs because they still have a share on said TCT (being co-heirs of the estate) and loan was made by only 2 siblings even if the 2 sisters have not the payment I'm demanding?

2.  What right do I have in order to compel the 2 sisters to pay me back?  Will a promissory note executed by the 2 sisters enough to put an encumbrance on the property?

3.  What legal remedy is best for me at this time to protect my interests?

4.  Can I be compelled to continue with the sale if they change the terms and conditions as per original verbal agreement?

The reason why I no longer wish to continue with the sale is because I no longer have any confidence that they will honor any terms and conditions I enter with them.

Appreciate if you could respond the soonest.  Thanks.

Questions:
1. Can I be compelled to turn over the TCT to the other heirs because they still have a share on said TCT (being co-heirs of the estate) and loan was made by only 2 siblings even if the 2 sisters have not the payment I'm demanding?

>> you cannot be compelled as it was voluntarily given to you.

2. What right do I have in order to compel the 2 sisters to pay me back? Will a promissory note executed by the 2 sisters enough to put an encumbrance on the property?

>> you have the right of a creditor. enforce the contract you signed with them before or file a demand for sum of payment for the loan plus interest they owe you.

>> with regards to encumbrance, you should have registered it with RD when you first entered into a loan agreement with them. im not sure if you can still do this but consult your local RD regarding the process/requirements.

3. What legal remedy is best for me at this time to protect my interests?

>> file collection of sum of money and damages (sila naman, for sure, mag de demanda yan ng specific performance to return TCT and damages sayo). be open sa compromise agreement sa arbitration later on. saka ihanda ang mga pictures ng bahay, before and after. ^^

4. Can I be compelled to continue with the sale if they change the terms and conditions as per original verbal agreement?

>> you cannot. if they do, kasuhan mo sila ng grave/light coercion, depende sa circumstances, may kulong yun.