我觉得应该是这样做吧：
WXML:
<checkbox-group bindchange="checkboxChange">
  <label class="weui-cell weui-check__label" wx:for="{{checkboxList}}" wx:key="{{item.value}}">
    <view class="weui-cell__hd">
      <checkbox value="{{item.value}}" checked="{{item.ischecked}}"/>
    </view>
    <view class="weui-cell__bd">{{item.value}}</view>
  </label>
</checkbox-group>

JS:
data: {
    checkboxList: [
      {value: '无', ischecked: ''},
      {value: '肝炎', ischecked: ''},
      {value: '高血压', ischecked: ''},
      {value: '糖尿病', ischecked: ''},
      {value: '高血脂', ischecked: ''},
    ]
},
let family_brothers_array = family_brothers.split(',');
var checkboxList = this.data.checkboxList;
family_brothers_array.forEach(element => {
  checkboxList.forEach(ele => {
    if(ele.value == element){
        ele.ischecked = true;
        this.setData({
          checkboxList:checkboxList
        })
    }
  });
});