Actually, the forsythia is probably the easiest! I can't imagine any problem with transplanting a forsythia to a reasonably warm climate (say zone 6 or warmer) this time of year. It's actually the best time to do it!

You also should not have any problems with the tiger lilies. Most sources recommend dividing them after the foliage has mostly died back and before new growth begins in late-winter. So, right now is also the time for that plant!

The iris might be a little more tricky. My only recommendation, if you have to do it now, would be to try to keep it a little on the dry side (very well-draining soil, etc). And, as always, be sure to plant it correctly...with the top half of the rhizome exposed (do not cover with dirt or mulch).