Yes, Russia does need Turkey's help to get parts of the Syrian opposition to negotiate. Turkey has been supporting some parts of the opposition forces (including providing weapons) since the start of the conflict. As these parts of opposition are partly dependent on Turkey for their survival, Turkey holds considerable power over them.
To the second part of your question: I have not seen any indications that Russia would wish to prolong the Syrian conflict or that it would take intentional steps which would increase the flow of refugees into Europe. The displacement of Syrian people has slowed down considerably after the catastrophe of 2012-2014 (when Russia was not yet engaged in Syria). 2012-2014 was the time of advancement of ISIS in Syria, and not even BBC tries to claim that Russia is responsible for that. Russia has taken several steps which have been aimed at de-escalation and at keeping the displacement of civilians internal to Syria. It has started the swaps of pro-government and anti-government pockets, separating the fighting sides and decreasing the intensity of armed conflict while not expelling significant number of people from inside Syria. It has conducted a long-term reconciliation programme. This is a slow but steady process practically invisible in the Western media. Recently it has initiated the de-escalation zones which could help the political negotiations in Geneva to start producing some results. There is some opposition to them (mainly because Iran is involved also) but they have the support of the Syrian government and Turkey (which controls significant parts of the opposition, see above) which gives them a chance to work. The de-escalation deal, of course, does not include ISIS or Syrian Al-Quaeda.
it is necessary to consider also Russian motives. I think the West greatly underestimates the weight Russia and Putin personally give to necessity to fight Chechen jihadists before they return to Russia. The Chechen conflict has always been of enormous importance to Putin, he's been fighting it since 1999 and never stopped. Another thing to consider is the cost of involvement in the Syrian conflict for Russia, which Russia can ill afford right now. Russia has achieved its most important objectives in Syria - keeping a naval resupply base in the Mediterranean and influence on European gas imports - and there's little the continuation of the conflict could add to them, except uncertainty.
