To isolate the turbos as a cause, pull off the intakes from the turbos, then the upper hot charge pipes from the compressor outlets, then, if necessary, the downpipes. Presence of oil in any amounts in these areas is a warning sign, though more elaboration is necessary:

If severe piston ring/cylinder wall/valve train wear is to blame, oil vapor may collect in the turbine housings and downpipes. Often the oil concentration is greater the closer you get to the cylinder heads, but nearly non-present in the exhaust ports due to the higher temperature. Small amounts of oil residue in the intakes and charge pipes is normal for relatively high mileage cars and/or those that have non functioning/poorly maintained PCV systems. Compressor/turbine oil seals will allow oil past into their respective housings. You'll be able to tell if the turbos are the cause. There will be significant oil in one of those areas; it will be quite obvious.