Q: Transfer iPad of family share member questions

We're giving mom's iPad to dad.  It is a cellular and wifi model.

He is the family share plan master account under his Apple ID.  She is a member of the plan with her own unique iCloud account and Apple ID.  She has unique contacts and messages and mail that she wants private to her iPhone.

I removed her mail and FaceTime and iCloud settings and added his.  Under the iCloud settings panel (this is iOS 9.3.2) is his name and ID.  There is also "Family" with her name and ID.

THis is loks the same under the "Mail, contacts, calendars" setting.

However, the iPad still recieves texts and messages sent to her, not to him.  And she claims that their contacts have merged.

i Suspect the texts (which are not distinguishable from messages from Apple devices, are they?) are simply people texting the number associated with the SIM card in the iPad.  I think the contacts probably didnt really merge.

is there any advice on how to best transition a device from one family member to another in the same family plan without sharing data from the previous owner?  If I remove her account under the iCloud and mail, contacts and calendar settings panels on this device, am I removing her Apple ID from the family plan altogether?  Or only on this iPad, and she remains in the plan on her lapto and her iPhone?

thx for any tips