It is very simple, but you can do it only in FTB, not in web interface. On your personal card in tree click Edit-Parents-AddParents and continue in dialog with second item.
I downloaded FTB and added my parents and merged the two trees together then exported the GEDCOM from that and imported it to my family web site. Now I'm not a child of my adopted parents any more and there's no link between me and my brothers and sister?
Does the web site not support that sort of relationship at all - am I ever going to be able to publish this so that both trunks of my family tree can be in the one place?
I do not know, why You are trying unnecessarily export Gedcom from FTB and next manually import to web? Web builder is very limited in comparsion to FTB. Its possible, not supports these complicated relationship. Web site supports it, but web builder not.
Publish tree direct from FTB and have no problems. This is situation, you must leave direct-shared web building, and start serious work in FTB.
I deleted all my web trees and started again publishing from the FTB but the whole point to this was to let my family update details and add people. If I end up no longer related to my brothers and sister then there's not much point.
Sounds like youv've been having hasles with it, my partner was also adopted & we know some info on his birth parents.
I've added them into our tree by clicking Edit on his profile, Click parents, click add parents, it will come up with a box click the second then add info.
When done it should read former last name on the persons page. Details of the birth family can then also be added,
My partner's box shows he has a former last name which was his birth name. I did this by clicking on EDIT, go to Parents, click ADD parents. This will then also have a box to tick to show which parents you want on the persons main page.
Once this is done you will find the names of both parents will be present in the EDIT section of the person. You will then also have to TICK a box to show which set of parents you want displayed, you will also have to mark them either apopted or natural.
I then clicked the natural parents and from there added children. Click attach exisiting child this will bring up a box showing pretty much everyone in your tree, add the person from there, or add as normal if they are not.
After doing this I now find my partner shows adopted parents him . Then when I bring up his birth name, the page shows his birth parents names his, but his adopted name shows because that is the box ticked.