There is no such thing as a Family Coat-of-Arms!
Coats-of-Arms were awarded to an individual person.
If you can prove direct linage from an arms bearer, then you are entitled to use them.
Otherwise you have no rights to us them at all.
This from the College Of Arms:
Q. Do coats of arms belong to surnames?
A. No. There is no such thing as a 'coat of arms for a surname'. Many people of the same surname will often be entitled to completely different coats of arms, and many of that surname will be entitled to no coat of arms. Coats of arms belong to individuals. For any person to have a right to a coat of arms they must either have had it granted to them or be descended in the legitimate male line from a person to whom arms were granted or confirmed in the past.
and
Q. What is a crest?
A. It is a popular misconception that the word 'crest' describes a whole coat of arms or any heraldic device. It does not. A crest is a specific part of a full achievement of arms: the three-dimensional object placed on top of the helm.