You indicate you are a co-tenant/seller with a sibling. Most escrows are held at the request of the buyer or buyer's title company pending payment of all estate taxes and/or the water & sewer bill, etc. It is unclear why your funds were placed into escrow, unless you really mean the attorney acted as your agent and the funds were placed into his attorney escrow account to be divided between you and your sibling.
I can well understand why the attorney would want to receive a release. As to your sibling, it is not uncommon in a release, to waive any and all claims now existing, whether known or unknown. You certainly have a right, although there seems no reason for you have done something to arise to a claim from the brief facts stated, for your sibling to provide a similar release and waiver of any and claims to you.
Without additional information, it is difficult to provide concrete advice. You need to consult an attorney. There are plenty in Jersey City, where I started my law career, or you can contact me at 973-994-9080.
The foregoing is not intended to be legal advice upon which you may rely as I have not been retained for this purpose.
As a co-owner, you do not have to sign a release of claims to get funds from a real estate transaction.
They are using the money as leverage.
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