In /etc/sysctl.conf file:
# Uncomment the next line to enable packet forwarding for IPv4
net.ipv4.ip_forward=1
Then update while running:
echo 1 > /proc/sys/net/ipv4/ip_forward
Add a route to wlan1 on the upstream Internet side
iptables -t nat -A POSTROUTING -o wlan1 -j MASQUERADE