Why didn’t Germany and Japan coordinate to attack the Soviet Union at the same time? Would they have been able to handle fighting on 2 fronts?

I've answered a very similar question here.

To summarise, while there was a strong drive within the Imperial Japanese Army (IJA) for war with the Soviet Union, the war in China had kept the majority of the IJA tied down, while--by 1941--the consensus among Japanese policy makers was solidifying around the Southern Operation, which would involve attacks on the American, British, and Dutch colonial holdings in southeast Asia. The Japanese-Soviet Neutrality Pact, concluded in April 1941, would serve to protect Japan's northern flank while it went south. When Germany embarked on Operation Barbarossa, some in Japanese leadership pressed for an immediate war against the Soviet Union (including Foreign Minister Matsuoka, who had just negotiated the nonagression pact with the Soviets), but it quickly became obvious to Japan that the Soviet Union was in no danger of collapsing in 1941, and that Japan should avoid being tied down in another large scale war on the Asian mainland, unless it was to pick up the pieces in the event of a Soviet collapse. To this end, the Japanese welcomed the German attack on the Soviet Union, as it basically ensured the Soviets would be unable to attack Japan as it embarked on its war with the Western powers.

One element I don't think I stressed enough in my linked answer is that Japanese leadership did not exactly trust the Germans in 1941. Until quite recently, Germany had been heavily involved in support for the Nationalist government in China, and many of the best Nationalist troops were German trained and equipped. In the political sphere, the Japanese had encountered a relatively recent "betrayal" at the hands of Germany. In 1936, Japan had joined in the Anti-Comintern Pact, which was supposed to ensure German-Japanese cooperation on anti-Soviet policy. However, from Tokyo's perspective, Germany had breached the treaty by signing the Molotov-Ribbentrop Pact in 1939, agreeing that Germany would not attack the Soviet Union. In Tokyo, this came as a huge betrayal, as suddenly the Japanese felt vulnerable, since it raised the prospect of a Soviet attack on Japan, without concern for a potential German attack. This apparent German betrayal soured Japanese attitudes towards Germany, and even when the Tripartite Pact was signed in late 1940, it included a clause that noted it did not impact any signers relations with the Soviet Union.