[Crystal Ambassador]

It's my understanding that you can communicate "at" them on your end just by thinking about or talking aloud to them, since they often hang around living loved ones. The tricky bit is being able to hear them in return.
I'm not one to encourage middlemen as necessary; I'm confident you'd be able to do it yourself, with practice. Honestly the practice is, to me, just a matter of developing sensitivity; like a person who becomes a musician can then hear more subtle things in music that they wouldn't have discerned before. There are a couple of guided meditations (audio or podcast) out there that are very helpful for meeting with passed loved ones, for focusing as well as structure.
For protection, I'd suspect that just asking whatever guide/guardian/deity you have to help protect you should be fine. You could also do a type of visual boundary if you'd like, where you envision yourself shielded in a protective energy that filters out ill intentioned spirits. Another option would be a physical energy barrier of some type; I've previously made a sort of circle of tumbled crystals on the floor that I sat inside that helped me feel more comfortable.
When I do journeys, I find the biggest help is intuition; if I encounter something posing as a helpful guide, they feel "off", like I can't completely trust that it's them for some reason. At that point I ask a guide (usually an angel, even though I don't generally work with them) to visit; their presence pushes the imposter away and creates a safe space to work within.

Many spirits have subtle ways of communicating as well; look for things in your regular life that "happen" to catch your attention. Coincidences. Words on signs you wouldn't normally notice. That sort of thing.

I wish you well, and I know you guys can get to the point of ongoing communication.