In early 2015, Juliana Santos, then aged 54, decided to sell her home in the Dandenong Ranges, of which she was sole fee simple owner, and move to Carlton to be closer to her workplace. By co-incidence, her adult son Carlos Santos, then aged 24, was at that time looking around for new accommodation because his landlord had indicated that his almost expired lease would not be renewed. Carlos wanted to buy a place of his own, but realised that he would be unable to afford it on his earnings as a backing musician.

Juliana suggested to Carlos that he should join with her in purchasing 48 Olympic Road in Carlton, which she had just negotiated to purchase for a price of $1,000,000. Carlos agreed. Juliana contributed $600,000 to the purchase price, being the proceeds of sale of her Dandenong Ranges home. Juliana and Carlos borrowed the remainder of the purchase price from Family Bank and assumed joint liability for repayment of the loan.

On 1 July 2015, Juliana and Carlos became registered as joint proprietors of the fee simple in 48 Olympic Road and moved in immediately thereafter. It was agreed between them that Carlos would be entirely responsible for paying off the Family Bank loan, although Juliana was jointly liable. As Juliana had a demanding job that required her to spend ten or more hours at the office each day, it was also agreed between them that Carlos would do the cooking, cleaning and other household tasks, while Juliana would pay all household expenses. They thereafter conducted themselves as agreed.

In 2017, Carlos, who had become a cooking enthusiast, decided that the kitchen at 48 Olympic Road needed a serious upgrade. Juliana was willing to indulge him. A kitchen renovation company quoted a price of $50,000 to do the upgrade inclusive of labour and materials. Upon receiving the quote, Carlos decided to do the renovation work himself instead. Juliana paid for all the materials needed for the renovation (an expenditure of about $25,000).

In April 2019, Carlos started dating Annisa Lestari. As their relationship progressed, Anissa got into the habit of spending the weekend at 48 Olympic Road, though she continued to live in her own apartment near her workplace in Bendigo during the week. Unfortunately, Annisa and Juliana did not get along at all.

On 6 June 2021, Juliana fractured her hip in a fall and was admitted to hospital for surgery and post-operative care. She was discharged from hospital 20 days later but, when she returned to 48 Olympic Road, she found that she could not get in because Carlos had changed the locks. Juliana, therefore, got a taxi to take her to her step-daughter, Maria Archarya's rented home in Thornbury. Upon arriving at Maria's place, Juliana asked Maria whether she could stay with her until the whole sorry mess with Carlos was sorted out. Juliana added, "If you let me stay with you as long as necessary, I'll give you half my interest in 48 Olympic Road." Maria, who was fond of her step-mother, let Juliana stay at her place.

Answer the following question, explaining your answers fully:

(1) What property interests, if any, do Juliana and Carlos have in 48 Olympic Road?