This question has been answered by lkfranklin. See the first response.
Hi Colln1981,
I haven't actually used the extra myself but on the face of it it looks to me like you need to use an additional extra called getids and set your &markers=`` to the parent ID of the resources you want to include.
https://github.com/jiripavlicek/gmaps/blob/master/modCategory/6e25da195b1962b069ff1502291c44c4/0/gmaps/docs/Gmaps100_v1.5.pdf
&markers=`[[getIds? &ids=`[[*id]], c[[*id]]`]]`
Did you set the parameters in the &marker to the parent and to also include children?
Try:
&markers=`[[getIds? &ids=`[[*id]], c[[*id]]`]]`
&limit=`0`
Whey great news.
Can you confrim that both 2 and 3 are published and not hidden from menus? Does it work if you set the call to both &markers=`2` and for `3` seperately?
I don't see any documentation for a limiter but its worth also trying
&limit=`0`