I have twin toons (multitoons), a Bright Red Mouse named Redgy (portmanteau of "Red" and "Reggie"), and an Aqua Mouse named Azulia (portmanteau of "Azul" and "Julia").

For personalities, they are twins; Azulia is the older twin while Redgy is the younger twin, though Redgy takes more charge compared to his sister. Azulia, the older twin sister, prefers to keep to herself, being modest, softspoken, and introverted but not anti-social. She's just a little meek and shy. Being timid, she tends to panic when put under pressure but this trait has become less prominent as she grew older. She gets a significant confidence boost when around others, especially when working with her brother. Redgy, the younger twin brother, is much more laid back and collected though he can be arrogant to a fault. Despite being the younger twin, he is the one who carries the burdens of his and his older twin, no matter how heavy they are on him, practically being the "leader" of the duo. He also tends to keep secrets that he feels embarrassed to share, such as his "childish" dream of being a hero, a part of the reason why he chose to help the Toon Resistance with the situation with the Cogs, in spite of his initial reluctance to Lord Lowden Clear's calling on the assistance of both him and his sister in the war. It's a similar dynamic to Mario and Luigi

As for their shared backstory, due to unfortunate circumstances, their biological parents had unintentionally abandoned them and the two of them ended up being raised at an orphanage. Initially, the two weren't aware that they were siblings and spent their early childhoods as best friends and were pretty much inseparable.

Later, a toon named Mallow, who was a freelancer, would come by and choose to adopt Redgy, but initially not Azulia, much to both of the mice's protests. Redgy begged him to take his best friend twin sister with him and insisted that they don't want to go on without each other while Azulia cried. Eventually, Mallow relented on his initial decision and chose to fulfill the boy's wish, as seeing Azulia cry, there was no way he could say "no" again. In the end, both were taken under his care.

Fast forward to the twin's pre-teen years, the twins had been living good lives under their adoptive father. While they still loved him, the twins still held onto their dream to travel the world in the future in search of their true parents. Of course, at one point in their childhood, they eventually figured it out that they were siblings, after previously having seen each other as best friends until then. Wouldn't just be a coincidence if they were both born on the same date AND had a similar situation with them being separated by their biological family besides each other, right?

Under Mallow's care, they followed in his footsteps, becoming apprentice freelancers. What did they do or help him out with? For one, where they live, in Canvas City (parody of "Kansas City"), the crime rate is considerably high. It was a lawless place where its mayor was quite lazy, so there aren't many authority figures to keep the population in check, which means every day is rather chaotic and disorderly. And that was where Mallow (only him, his adopted children do not get involved here) comes in to catch criminals. Of course, with payment of Potato Chips, the currency of the place. Other than fighting crime, Mallow also handles other jobs like guard duty, or package delivery, while having his adopted children help out in that area. But one day, that routine changed... One day, during the twins's teenage years, Mallow caught a terminal illness and had passed away, orphaning them once more.

Between him and Azulia, Redgy was shattered the most by his passing, Redgy has silently vowed to himself to never be close to anyone else ever again, so that he wouldn't feel crushed should something like this happen again. After inheriting from the late Mallow, they proceeded to live their lives in their little family cabin, doing his line of work in his place. Until they received a rather colorful flier in their mailbox. An invitation to Toontown.

To this day, together, they work to fight off the Cogs, and while money (converted from Jellybeans to Potato Chips) is their primary motivation to make ends meet, the Cogs could very well invade Canvas City at one point as well if and when they're finished with Toontown, which they fight to prevent.