What your husband is asking you to do is with regards to the DEEN, therefore, in such cases the first and last order belongs to Allah and His Messenger.
"It is not for a believing man or a believing woman, when Allah and His Messenger have decided a matter, that they should [thereafter] have any choice about their affair. And whoever disobeys Allah and His Messenger has certainly strayed into clear error." Surah Ahzab (33:36)
Also the famous saying of the Prophet(salallaahu ‘alaihi wa sallam):
"La ta’aata lil makhluk fi ma’seeyit al-Khaaliq (which means there is no obedience to the creation in disobedience to The Creator.)"
Therefore, If a “scholar” (or imam of your masjid) or your husband advises you to disobey Allaah and His Messenger (salallaahu ‘alaihi wa sallam) by telling you or giving you “permission” to call on other than Allaah, or say that Allaah in His Self is “everywhere,” or rebel/speak ill of the Muslim ruler, or celebrate the Prophet’s birthday, or engage in ribaa (interest, usury), then in these particular cases obedience to that “scholar” is disobedience to Allaah. (http://salaf-us-saalih.com/2013/04/04/there-is-no-obedience-to-the-creation-in-disobedience-to-the-creator/)
Moreover, there is no established sunnah of the acts which you mentioned done by the Prophet or his Sahabah and thus are is a Bid'ah. Also, as you already know that these acts (such as maulid, drinking washed slate writings, consulting mallams who tell us that some relatives are responsible for my inability to conceive, etc.) is wrong, then I don't think I need to provide evidences that these acts are wrong.
And Allah knows Best