Tricky Q on tax payable on PPR/Investment Property

MY 2 Friends bought a house 3 years ago, 1 of them recently bought another with her partner, as such she wants to pull her mortgage interest relief from the 1st house she shares and use it on her new home-which will become her PPM,
this leaves the property she owns with her friend as an investment property BUT is this viewed as an investment property or PPM for the 2nd friend?

Secondly, if the house is sold would the 2nd friend be liable to pay CGT on her portion of the profit?

THis is happening for 2 friends of mine and my concern would be the 2nd friend will be given the short end of the stick big time.

So i guess my main question is can a house with 2 owners be seen as both a PPR and an investment property or do revenue just view it as one?

Friend 1 - Investment property, CGT payable on sale.

Friend 2 - Remains as PPR and can avail of PPR relief from CGT.

Property can be both an investment and a PPR in this situation.