Firewall, NAT, Quad Card

I’ve got a quad card on a firewall

1st link to my internal segment
2nd link to my DMZ with external IP addresses
3rd link to the Internet
4th link to my databases with Internal IP addresses

Question is… can I allow external users to link to my databases on the 4th ethernet port via NAT?

If so… can that NAT-ed external IP address be part of the subnet range of my 2nd link? I am only given a few public IP addresses and I am unable to subnet it further. The only way is to use oneof the IP address which is currently available from my 2nd link (does this sound confusing)

Can this be done?

I’m using Checkpoint and am wondering whether I should add a route and arp on the firewall after adding the rules for the NAT.

Please advise.

Thanks