when it comes to your BIL, be careful not to pay to much or put too much pressure on him. i would probably try to win him over, let him see the good in you and what your H left behind. hopefull he will go back and tell H he is being a shmuck for what he is doing to you, rather than go back and tell H you were prying for info. in other words, be yourself, be calm, be happy, be positive. Be everything you want your H to find out about you.
As for the MIL... how dare she! if they are not going to be nuetral parties or help with what is right, then they should stay out! Does your H really need his mother fighting his battles or talking for him. H is just using your words against you to validate his fears and feelings.
Hope H writes back soon! and would be really nice if he made the MC appointment.