Oh dear this sounds unnecessarily arduous!
I don’t have and as far as aware no need to have gmail account to be on WhatsApp?!
Also WhatsApp is mainly a phone messaging service - albeit using WiFi as opposed to phone signal - and my iPad isn’t that old but still don’t think I could get it on there...
Hope you now have it it’s easy to use it should be!
My beloved grandad died a year ago this month aged 92yo but he managed to master FaceTime and WhatsApp etc easily so it is possible

Tended to leave his phone off and at home but that’s another issue LOL!