How to implement guest wi-fi on Mikrotik?

Question

Mikrotik

So what do we have.
2 providers (the first is connected via staticIP, the second via DHCP)
MikroTik RB951G-2HnD, and Unifi
At the moment, 2 wi-fi networks have been created, one guest (by unifi). The Internet goes to these networks through provider 1.
What you need is to set up Mikrotik with two providers in such a way that the Internet from provider 2 is simply distributed to the guest wi-fi, but at the same time, if necessary, there is access from the main network to the local resources of this provider .(TTK internal network)
At the same time, you need to take into account that Ipsec (as well as pptp and gre) tunnels are already working on Mikrotik through the external IP of the 1st provider, several vlans are configured.
Well, then it remains only to configure unifi to work with the necessary vlan on Mikrotik.
Main questions.
1. How to implement isolated operation of guest wi-fi in my vlan using Internet provider 2, but at the same time leave access from other vlans to the local resources of the provider. And so that the tunnels do not collapse at the same time.
2. Can it be better to combine Internet channels, and completely lay the control over the guest network on the shoulders of unifi?
3. Or maybe there is an even more elegant solution?