@hyacinth003
At this point you've had this discussion too many times with your nosey SIL and your spineless brother, to think that their (HER) continued interference in YOUR duty as executor, is not deliberate.
He seriously needs to grow a pair and deal with his wife, to impress upon her that the estate (you, as executor), having to retain an attorney to deal with them, will only REDUCE the amount of inheritance they will receive.
I believe you mentioned before that your Dad wouldn't want his estate to be drained by attorneys battling for opposing family members, as had happened in his family in the past, but they're giving you no choice.
Maybe a good ol' 'come to Jesus' meeting with your BROTHER, not his Battle-axe wife, would help them see the light.
If not, an estate paid attorney and billing the estate for you performing the duties required as executor, may be your only choice with these two.
Just my opinion, but do keep us posted!
You never know how strong you are until being strong is the only choice you have.