For a start I would highly recommend you to upgrade Junos to the recommended JTAC release. There were quite some bugs in the 15.1X49-D70 Junos version.
Secondly you have configured dhcp both the old and new way and only partly configured the new way.
Suggestions to your configuration:
1. Please remove anything below "system services dhcp" and "access address-assignment".
2. Add the following config lines and commit.
3. Validate and revert with the result here.
set system services dhcp-local-server group int interface irb.8
set system services dhcp-local-server group int interface irb.9
set access address-assignment pool int family inet network 192.168.8.0/24
set access address-assignment pool int family inet range scope low 192.168.8.30
set access address-assignment pool int family inet range scope high 192.168.8.99
set access address-assignment pool int family inet dhcp-attributes grace-period 86400
set access address-assignment pool int family inet dhcp-attributes name-server 207.164.234.193
set access address-assignment pool int family inet dhcp-attributes name-server 198.235.214.4
set access address-assignment pool int family inet dhcp-attributes router 192.168.8.1
set access address-assignment pool int family inet network 192.168.9.0/24
set access address-assignment pool int family inet range scope low 192.168.9.30
set access address-assignment pool int family inet range scope high 192.168.9.99
set access address-assignment pool int family inet dhcp-attributes grace-period 86400
set access address-assignment pool int family inet dhcp-attributes name-server 207.164.234.193
set access address-assignment pool int family inet dhcp-attributes name-server 198.235.214.4
set access address-assignment pool int family inet dhcp-attributes router 192.168.9.1
I hope this helps - and remember to upgrade your SRX 🙂