I've been trying to find a tool (that works) that will enable me to auto post to some of the FB groups that I am member of - without being an admin. Sadly I tried safeposter, but the credentials never worked and the support, well wasn't there. Is there anything else?
Used to use buffer. Used Falcon.io too. There's tons of tools out there doing this, you will find that they sometimes stop working or remove features, because Facebook is always updating their API's etc and removing access to stuff.
Why is everyone recommending Buffer? OP isn't an admin of any of these groups so Buffer is useless. Check out https://jarvee.com it'll do everything you want and more.
Check out ubot studio. That will do the trick. I think they may also have a bot already built. It is a great tool