If there is only one person who overlaps in both trees, then you can merge them manually. Here's a previous post that explains how to do it. If you're not comfortable doing that, there are programs that merge two GEDCOM files together. Here's an article from Family Tree Magazine that looks at a couple of them. It turns out that merging two family trees is a pretty common thing for people to want to do, and if you search on Google for "merging GEDCOM files", there are a lot of resources to look at.
As far as losing any of the fields in Family Echo, you can see what Family Echo exports as part of the GEDCOM file by downloading one of your family trees as a GEDCOM file and then reimporting it. But my recollection is that everything except pictures are exported.
