Honestly, I find myself in this situation a number of times almost every match for throw-ins as I do games solo. Legs flying, rebounds or grazing legs or boots on way out. Actually, I made a throw in call Saturday on a best guess as there was a bunch of players around the ball as it pinged out. When I made the call, I knew from the reaction of some of the players that I called it wrong. I immediately changed my mind and called it the other way. A couple of players were miffed with one saying I couldn't change my mind. I told him Yes I can and get on with it.
Normally I just call it and as I see it and if there is lots of complaints I tell them I if I'm wrong I apologise but I'm not changing my decision.
Anyone who argues with that gets a stern talking to and a last warning.
So my advise, not knowing the situation in your part of the world - get the coaches to do the line but tell them you'll make the call. If you are stuck, ask them (they'll likely tell you everytime anyway which is good, as you'll spot who is honest and not). However, if you can't do that, just make a call the best you can and stick with it right or wrong.