What are the Sharif's options?

This piece says the Sharifs could "surrender" by appearing before the court without surrendering before the police.

"The Sharifs do have the right to appeal under Section 32 of the National Accountability Bureau (NAB) Ordinance before two judges of the Islamabad High Court (IHC). The IHC has inherent powers to accept the appeal, suspend the sentence(s) pending appeal and/or overrule the authorities’ sentence. Convicts who do not surrender after their conviction generally cannot file an appeal.

Read more here.