There are several utilities to handle doing this recursively for you but assuming all you have is dbus-send you can still accomplish what you are trying to do with the following:
Take the list of services and for the ones you are interested denoted by $SERVICE in run:
dbus-send --session --dest=${SERVICE} --type=method_call --print-reply "/" org.freedesktop.DBus.Introspectable.Introspect
This will give you something like:
method return time=1563564828.143670 sender=:1.107 -> destination=:1.13227 serial=167 reply_serial=2
string "<!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
"http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
<!-- GDBus 2.58.3 -->
<node>
<node name="org"/>
</node>
"
For each node node you can run the command again for the subpath so for NODE_PATH=/org
dbus-send --session --dest=${SERVICE} --type=method_call --print-reply "${NODE_PATH}" org.freedesktop.DBus.Introspectable.Introspect
You would get another set of nodes with which you can repeat the process until you finally get to the interfaces which list the methods. Here is an example:
dbus-send --system --dest=org.freedesktop.DBus --type=method_call --print-reply "/org/freedesktop" org.freedesktop.DBus.Introspectable.Introspect
method return time=1563565305.203169 sender=org.freedesktop.DBus -> destination=:1.13267 serial=3 reply_serial=2
string "<!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
"http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
<node>
<interface name="org.freedesktop.DBus">
<method name="Hello">
<arg direction="out" type="s"/>
</method>
<method name="RequestName">
<arg direction="in" type="s"/>
<arg direction="in" type="u"/>
<arg direction="out" type="u"/>
</method>
<method name="ReleaseName">
<arg direction="in" type="s"/>
<arg direction="out" type="u"/>
</method>
<method name="StartServiceByName">
<arg direction="in" type="s"/>
<arg direction="in" type="u"/>
<arg direction="out" type="u"/>
</method>
<method name="UpdateActivationEnvironment">
<arg direction="in" type="a{ss}"/>
</method>
<method name="NameHasOwner">
<arg direction="in" type="s"/>
<arg direction="out" type="b"/>
</method>
<method name="ListNames">
<arg direction="out" type="as"/>
</method>
<method name="ListActivatableNames">
<arg direction="out" type="as"/>
</method>
<method name="AddMatch">
<arg direction="in" type="s"/>
</method>
<method name="RemoveMatch">
<arg direction="in" type="s"/>
</method>
<method name="GetNameOwner">
<arg direction="in" type="s"/>
<arg direction="out" type="s"/>
</method>
<method name="ListQueuedOwners">
<arg direction="in" type="s"/>
<arg direction="out" type="as"/>
</method>
<method name="GetConnectionUnixUser">
<arg direction="in" type="s"/>
<arg direction="out" type="u"/>
</method>
<method name="GetConnectionUnixProcessID">
<arg direction="in" type="s"/>
<arg direction="out" type="u"/>
</method>
<method name="GetAdtAuditSessionData">
<arg direction="in" type="s"/>
<arg direction="out" type="ay"/>
</method>
<method name="GetConnectionSELinuxSecurityContext">
<arg direction="in" type="s"/>
<arg direction="out" type="ay"/>
</method>
<method name="ReloadConfig">
</method>
<method name="GetId">
<arg direction="out" type="s"/>
</method>
<method name="GetConnectionCredentials">
<arg direction="in" type="s"/>
<arg direction="out" type="a{sv}"/>
</method>
<property name="Features" type="as" access="read">
<annotation name="org.freedesktop.DBus.Property.EmitsChangedSignal" value="const"/>
</property>
<property name="Interfaces" type="as" access="read">
<annotation name="org.freedesktop.DBus.Property.EmitsChangedSignal" value="const"/>
</property>
<signal name="NameOwnerChanged">
<arg type="s"/>
<arg type="s"/>
<arg type="s"/>
</signal>
<signal name="NameLost">
<arg type="s"/>
</signal>
<signal name="NameAcquired">
<arg type="s"/>
</signal>
</interface>
<interface name="org.freedesktop.DBus.Introspectable">
<method name="Introspect">
<arg direction="out" type="s"/>
</method>
</interface>
<interface name="org.freedesktop.DBus.Peer">
<method name="GetMachineId">
<arg direction="out" type="s"/>
</method>
<method name="Ping">
</method>
</interface>
<node name="DBus"/>
</node>
"