I believe providing a brief intro of each of your family members will not have any adverse impact on your case. if any advantage you have to get, the VO should get enough time to read throu your write-up. there is no harm.
For what? VO/CHC do not spare time to read any junk explaination or which is not required by VO/CHC or which is not asked to submit by VO of your local CHC. there is no negative impact on your file. but why you want to describe those part which is not required by CHC or not mentioned by CHC. If VO/CHC ask you to submit any proof or in written then you can submit those documents. No need for cover letter regarding you mentioned in your post.