Is it permissible to give charity to a married sister and her children while her husband is alive, and is it a condition for this that the sister be poor and in need?

Voluntary charity given to a sister is permissible in all cases. As for obligatory Zakat, it is not to be given to a sister who is self-sufficient, either by herself or through her husband. However, it is permissible to give it to a needy sister whose husband is poor or does not provide for her. This is better than giving it to a non-relative, as the Prophet, peace and blessings be upon him, said: "Charity given to a relative has two rewards: charity and upholding kinship ties."