All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The normal and ordinary love of some non-Muslims does not affect faith and does not undermine its validity.
For example, loving a non-Muslim because he/she is a relative or for his/her kindness to you, and for other reasons. Allah Says to His Prophet (what means): {Indeed, [O Muhammad], you do not guide whom you like, but Allah guides whom He wills.} [Quran 28:56]
Your family are Muslims, praise be to Allah, so there is no need for these whispers and doubts about their Islam.
Nonetheless, you and your family should endeavor to guide your apostate brother hoping that Allah will guide him.
For more benefit, please refer to Fataawa 369664, 384016, 333871 and 375391.
Allah knows best.