ISP BGP QUESTION

Hello Everyone. We are planning to decommission our two old BGP Routers and replace it with a Fortinet Firewall. We have two internet service providers on which we are advertising a /24 prefix using those two BGP Routers.

My question is, is it possible that our two internet service providers can advertise our /24 prefix on our behalf using our own company AS numbers? Then the two ISP will just route the /24 back to us using a static route?

My networking knowledge tells me that this is not possible because of the following: but still, I wanted to confirm with you guys.

1. Those two ISP cannot advertise the /24 prefix for you using your own AS number. It has to be their own AS.
2. The /24 prefix cannot source from two different AS from the two internet service providers.
3. Failover is not guaranteed to work, or will not totally work.
4. Asking an ISP to advertise a prefix for you to the Internet is ok, if we have just one ISP.... but since on this case we have two ISP, this is not possible.

Please let me know if this is correct, if not, please explain why.

Thank you so much!