DH lost his mum a while ago. Very sad but not unexpected. DH told my parents, and DM said that she would let my DSis know when she spoke to her the following day.
I thought I would hear something back from DSis some time during the following week. When DBIL's father died last year, we sent a nice card and flowers for the funeral. We didn't hear anything though, so I thought perhaps DM had forgotten to mention it.
I rarely talk to DSis myself as she doesn't answer her phone and always forgets to return calls. She is usually terribly apologetic about this, but I've concluded that she can't really be bothered, so now I don't hassle her. However, DH rang DBIL the other day with some info about some possible work for him (he is self employed and desperately needs the business). At the very end of the conversation, DH told DBIL that his mother had passed away (several weeks ago now), and DBIL said "oh yeah, we were sorry to hear that, DMIL told us at the time." 
AIBU to have expected some acknowledgement from them if they knew what had happened? They knew that DH was incredibly close to his mum, and I feel quite embarrassed at the fact that they appear to have just ignored it. Is it not normal to send a sympathy card or something in circumstances like this?