Yes, counseling, now. Do not wait. Counseling is for BOTH you and him, together, not just for you. Will he be willing to do it? If not, you may have to talk to him about how counseling does not mean he is "broken" or "weak" -- some men see counseling or therapy as being only for weak men, or as letting a stranger know their private business, but you have to get him past that and into counseling with you.
The fact that you say you don't know if he's happy tells me that you and he do not communicate well. Please, please see a professional to learn communication skills so you CAN find out if he's happy. And so you can learn to tell him, "I feel that you don't stand up for me with your family."
Is he originally from a culture that is different from yours, or a culture where family members expect certain other family members (father, or eldest son, etc.) to provide and care for extended family even after marriage? Is it possible that his family is just not accepting that he does not play that role for them, culturally? Or is this just plain old greed, as in, "Where's our money?"
Please get counseling so you can get tougher, yourself, and not feel hurt by his family's cruel and silly comments like the one about spending their dad's money. How did you even know that comment got made? You said you "saw" it so I assume maybe you were on the sister-in-law's Facebook page and she posted it, or you were on another social media site where she posts, or you somehow saw an e-mail she sent to someone else -- not you? I would stop all Facebook and other social media with family members; if it stresses you out, why do it? They may say, "You're so anti-social, you don't 'friend' us or 'like' us online!" but you can reply -- especially if counseling teaches you to be assertive -- "Well, I'm cutting back all the social media stuff to have more time for other things, and there is always e-mail direct to me if you want to reach me individually. From now on I'll be e-mailing folks individually, or phoning." I think dumb posts on Facebook and other media are the source of much of the family drama these days so just dump it-- if they go on social media and complain about you there, you don't need to be reading it.