I have long experience with angels, and I have good and bad news for you.
The good news is yes, you can put two juneniles together and they should be just fine. The bad news is that long term, your tank may prove to be too small for both of these fish to live together. Both reach large sizes, albiet not so large as in the wild. I would suggest adding both of these fish at the same time if possible, and making sure they are both larger than the flame angel if the flame is already present. 3-4" is a good size.
Some people like to go on and on about how large an emperors and queens get, and that you shouldn't put one in anything smaller than a 300 gallon, blah blah blah. Most of these people have never kept an emperor at all, let alone for the years it takes to even make a statement one way or the other. The truth is that most angels, (note I said MOST) grow to a certain size, then slow WAY down in their growth rates in captivity. An emperor, if fed an nutritious diet, can be expected to grow to around 9" or so before growth starts to slow. A queen is similar in this respect, but it may get to 10 or 11" before it slows. An exception would be the french angel which will go from the size of a nickle to a foot long inside of a year.
Back in the day when I kept fish only tanks, I had an angel community in a 180 gallon. This tank housed a queen, a french, an annularis, an emperor, a blueface , a personifer and a lemon peel and a koran.
They did just fine for about a year and a half, then I had to start thinning them out as the french just got huge, and there just wasn't enough space.
Regards
Jim
