Group texts will behave differently according to how your message app is set up (and possibly how theirs is set up), and worse when sending across platforms. There are 2 issues here:
1) Your Android SMS/MMS app will have a setting for whether to use SMS or MMS for group chats. These behave differently: with SMS you send separate messages to each person, and each replies to you separately. It's not really a group chat. MMS behaves the way you want (everyone received every message), but in some countries/provider MMS are expensive so it may be that not everyone sets their app to use them for groups (in the UK for example SMS have been effectively free for almost everyone for most of the century but MMS remain crazy expensive. I get the impression that in the US SMS were charged for for much longer but there was less difference between MMS and SMS). In any case, if people have their apps set differently you can get different behaviour.
2) iPhone use iMessage. Between iPhones that works similarly to WhatsApp etc: advanced features (e.g. you can see whether a message has been read, when someone is typing a reply), higher quality media than MMS supports, etc. But iMessage is Apple-only (a choice Apple made because they felt it offered a competitive advantage - or "lock in" some some would call it). So when you have a group chat that crosses platforms the iPhones will send MMS or SMS to the Android users (presumably they have a setting to determine which), and so those people end up as "separate" from the iMessage users.
It sounds like it was the second that was your main issue. In which case nothing will have changed: iMessage is still Apple-only, so will treat Android users differently.
Will Google Messages resolve it? To be honest, I doubt it. The new(ish) thing in Google Messages is RCS, a more advanced messaging protocol that behaves a bit like iMessage. Unfortunately it also behaves like iMessage in that it only works between Android devices (because Apple refuse to support it, presumably for the same reason they didn't make iMessage cross-platform). So presumably iMessage users will still send either SMS or MMS to Android phones, and Google Messages will still send either SMS or MMS to iPhone users. In fact since some Android users may not be using RCS it could actually make things more complicated (I'm one of them: I know nobody who uses it, and it doesn't work between platforms, so I've never felt it was worth enabling personally). But I certainly don't see how it will solve the problem of different behaviour between platforms.
So, that all sounds very pessimistic. What's the solution?
It might be that if everyone's apps fell back to MMS when their preferred protocol wasn't available it would all work, but if it didn't then I don't have much confidence that it will now (I'm British, nobody I know is willing to spend £0.50/message, so I've never been involved in an MMS group chat, and hence can't say from experience). Everyone I know solves this by using a third party app such as WhatsApp (or Signal, or whatever you prefer): it requires everyone to have installed the same app, but once they have it will work the same whatever phone they have, and with none of the hassle you get from different people's apps, especially on different platforms, behaving in different ways. If Apple opened up iMessage, or allowed RCS support on their phones, then we'd have a built-in cross-platform solution, but as long as they refuse to support that then you will get the best experience by using a third party system (I'm not being biassed here: I do use Apple devices as well as Android, but both of those options were rejected by Apple, not by anyone else, so I'm afraid the lack of a good native solution is their choice).
