Hi guys,
I run a basic hotspot off an old wAP for some years now with no problems. Internal user database is used for simplicity as there is only one user (free/free). A wired ADSL modem is the gateway behind it.
WLAN interface IP 10.30.30.1 with hotspot DHCP Pool is on 10.30.30.2-50 and its wired connection to the modem on 192.168.1.10 through a switch.

Now I needed better coverage upstairs so I got a cAP ac (wired on the same 192.168.1.x switch) for that but I am trying to share the same hotspot, pool and "session" so that users don't need to reauthenticate when roam from the wAP to the cAP upstairs and vice versa.
Is this possible? Any guidance would be appreciated?

1) WiFi is not GSM.

2) read and understand all passages before do anything
3) use winbox by MAC, not IP, if possible
4) temporarly disabe wifi on cAP ac, or change SSID to don't be equal to old wap, and program it by ethernet
5) set EoIP tunnel between the 2 AP, one with 10.0.120.1/24 and other with 10.0.120.2/24
when both ping eachother:
6) on cAP move any dhcp-client or IP address from bridge, if any, to ether1
7) delete first any port on bridge, then bridge itself on cAP ac
8) on new AP create one bridge and put inside wlan1, wlan2 and EoIP
9) create on old wAP one bridge, add ONLY EoIP for now
10) move hotspot service port from wlan1 to new bridge
11) move dhcp-server, if any, from wlan1 to new bridge
12) move IP address, assigned to wlan1, to new bridge
13) put now inside wAP new bridge the wlan1
14) set on new router wlan1 and wlan2 with same parameters (when possibles) of old wAP wlan1

done.

Wow... was not expecting that detailed answer. Will try and report here and mark it as answered if I get it to work.
Thank you so much!