Good for you and for your husband for standing up to them.
When things calm down a little bit, and it's a quiet moment, thank your husband for standing up to them. Tell him that you can't imagine how hard that was to do, and that you know he is hurting because of it, but that you are proud of him and love him even more for defending and protecting his baby daughter from an unsafe situation. He supported you and the baby, now support him as he struggles with this. Show him (physically if need be) how much you love him and respect him as the provider and defender of your family.
You spoke of having other arrangments for daycare-make those arrangements. Then wait a few weeks, and invite the family over for a picnic (check with your husband if he thinks its a good idea), and extend that olive branch to them. Smile, and keep smiling, and don't let them goad you into retaliating against them.
Whatever else they may think/feel, they are probably really hurting right now and may be in denial about the Altzheimer's -- it's a devastating disease and they are all suffering, and you're probably the easiest scape goat they can find to blame (instead of dealing with their feelings about the Altzheimers). If your husband can/is able, he should join a support group for family members of Altzheimer patients, and encourage hims mom and sister to do the same.