Problems with group texts

I created a group text for 10 people on 11ProMax. All 10 got the texts. Then 1 person needed to be removed but I couldn’t remove her. I discovered it was because she wasn’t an iPhone user. Weird since I had no problem including her in the original setup of the group. So I had to start a new group. Then 1 person (who had been in the first group wanted to be added to the second group. But I couldn’t add her because she’s not an iPhone user (message says she’s not registered with iMessage). O. M. G. This is ridiculous. If I can include contacts without any problem when first setting up a group, I should be able to just as easily add and remove regardless of what kind of phone they have.