The Bible seems to indicate that only God has the attribute of omnipresence. See Jeremiah 23:24
If we are able to contact the saints in Heaven, it would be necessary that they also be omnipresent for our multiple requests to them to be successful.
We know that Satan is not omnipresent, since he must “roam to and fro” about the earth and he needs his minions to help him in his warfare against God and us.
The angels also appear to be limited “presence-wise” as was demonstrated by the angel sent to Daniel taking twenty-one days to make it. See Daniel 10:13
I recall Jesus saying that we would be like the angels in Heaven when talking about marriage and divorce etc., so I might be wrong in assuming that other angelic attributes also apply generally. Our dying “in Christ” will likely give us greater attributes than even the angels, but I question the omnipresence attribute which is a “God attribute only” in my understanding. (There goes that “only” word again.)
Maybe someone could point out what I’ve overlooked in the Bible that could explain where the saints in Heaven might have the needed attribute of omnipresence to respond to multiple prayers. I’m sure that some saints are supposedly getting millions of requests per second from millions of different locations on earth.