Am I able to have multiple copies of Molten Nursery out at once and will their abilities stack? For further clarification, let's say I have two on the field and I play a colorless spell, would both copies each do one damage?
If you control more than one Molten Nursery, the triggered ability of each one will trigger whenever you cast the same colorless spell (C.R. 603.2; see also C.R. 113.2c). In general, there is no limit to the number of permanents with the same name you can control.
Molten Nursery Stacking