this might be a dumb question but here it goes…is it possible to have siamese triplets? i was watching MP and the Holy Grail and they had the 3 headed “monster” that argued with itself and that inspired me to find out from the teeming millions if anyone knew of siamese triplets. Or even siamese quadruplets? have any been born but never survived? is it even biologically possible? Or whar about this far flung idea: a set of twins who are also siamese twins- picture the famous siamese twins-chang and ang- and then have another identical set of chang and ang. thanks.
I have never heard about this, and the reason I went to medical school was for the freaks. 
So I would probably have seen pictures if it did.
It could probably happen, but it would be very rare and I would be very surprised if it was actually viable. Siamese twins are caused by a relatively late splitting of the embryo with incomplete separation. This is the same process that leads to identical twins. Identical triplets IIRC are fleetingly rare, and this would be a very rare form of identical triplets. The earlier monozygotic twins split, the more viable they are. The earliest split leads to two placentae with two blood supplies. Later splits lead to some shared membranes, then even later one cause all shared membranes. The latest are conjoined twins. Even monoplacental twins are wrought with complications during pregnancy, delivery, and postnatal care. Much worse is to be expected in triplets.
There are already a bunch of columns on twins, both by Cecil and the Staff. Here are some:
Siamese twins
Identical twins/identical DNA
Five kinds of twins
Identical twins/identical fingerprints