Is it possible to have 1:M:1 and 1:M:M forms

Hi,
If you don't create a "placement" you should use a list instead of a subform.
Otherwise :
In form create an independent textbox named HF_ID. No link field !
In subform placement on current_form event use this code :

if not isnull(me.HF_ID.value) then
    'copy placement number in new HF_ID textbox in form
    me.parent.HF_ID.value = me.HF_ID.value
endif

In form select container of subform hostfamily, in properties LinkMasterFields and LinkChildrenFields write 2 fields of the (new) relation :

LinkMasterFields : Sdt_ID;HF_ID
LinkChildrenFields : Sdt_ID:HF_ID

If you are refresh problem on host_family subform add this before the Endif instruction.

Me.Parent.Controls("sfHostFamily").Requery

sfHostFamily is the name of CONTAINER of subform and not name of subform.