With any degree of proper preparation? Yes. The Royal Yugoslavian army isn't fit to fight any one of those countries, let alone all three.Say Italy invade Yugoslavia instead of Greece with Hungary and Bulgaria joining
Would Italy be able to conquer Yugoslavia without Germany support
Don't forget about Zara, some harassing actions followed by protracted resistance could be launched from it.There are two landroutes for the Italian Army into Yugoslavia. From Albania in the south and into Slovenia in the north. There was only one avenue of attack against Greece.
Italy's contacts with Croatian nationalists are also stronger than Germany's were, and they could also play up the fact that the Queen of Italy was Montenegrin Royalty to foster division amongst the Serbs.Yugoslavia was a pretty divided country. It also had a Italian minority on the coast.
They actually wanted to, but Germany was not in favor, so Mussolini backed off.Say Italy invade Yugoslavia instead of Greece with Hungary and Bulgaria joining
Would Italy be able to conquer Yugoslavia without Germany support
In the last two years before the start of World War II, Italy almost broke off diplomatic contact with Yugoslavia and started negotiations with Germany and the Ustaše. Italy recalled General Gambara from Spain in 1940 so that he could take control of forces which would attack Banovina of Croatia (a Yugoslav province).[5] This offensive was only delayed because of the Italian declaration of war against France on 10 June 1940. Italy created plans of attack on Yugoslavia in February 1940 with the primary objective of taking Šibenik, Split and Kotor so that the Adriatic situation would be eased. The only problem with this plan was that Hitler wanted to create an alliance between the two kingdoms against Greece. During negotiations in late 1940, Italy offered Thessaloniki to Yugoslavia but it was rejected. Only when Hitler put forward a similar offer in March 1941 was it accepted, and Yugoslavia become a member of the Axis powers on 25 March 1941. Hitler ordered an attack on Yugoslavia following the coup d'état on 27 March; two days later the new Yugoslav prime minister, Dušan Simović, asked for Italian help in restoring relations with Germany. Simović warned Italy that Yugoslavia would overrun Italian Albania if the Axis powers declared war.[6] This war would start on 6 April 1941 and end with the destruction of the Yugoslav Kingdom on 17 April.
Well not piling up bodies on France's door step and being able to recall forces from North Africa would tilt the balance in even more in Italy's favour, but then I suppose the question is then what Hitler will do in response. He doesn't even necessarily have to do much to draw out that conflict, simply encouraging Slovakian and Romanian aggression could take the wind out of the sails of Hungary and Bulgaria.To do this Italy would basically have to opt out of WW2 and an alliance with Hitler...which might create some problems.
Not really given the huge economic interests that Germany had in Yugoslavia. They spent a lot effort courting Yugoslavia into the Axis for a reason; it might well provoke a war between Germany and Italy if Mussolini invades Yugoslavia and seizes it's resources given how much it would negatively impact the German war economy if Italy disrupts shipments of goods.Wouldn't Hitler view a Italian-Yugoslav war as a distraction and leave Mussolini alone? His goal was to exterminate the Soviet Union not get bogged down in a Balkan War.