While the Sansevieria is a slow grower, giving it good light and prescribed fertilisers can increase its growth rate. As for the Areca palm, like any plant it will grow faster with sufficient lighting and slower in low to medium light. Although, avoid direct sunlight for both the plants.
Brown raised on areca palm
The Areca palm is fuss free in general but is susceptible to scales. If you see small brown raised dots on your plants, it is a scale infestation. Use a toothbrush and water to scrape the scales and then spray them with an organic pesticide like neem oil. Repeat the process weekly for a month for a healthy plant. Neem oil can be sued every 15 days as a preventive measure for all plants.
Wilting of Sansevieria
Sansevieria is a drought resistant plant and does better with underwatering than over watering. Limp, wilting, and mushy leaves are a sign of root rot due to overwatering. If the plant is fairly erect, repot it in a drier potting mix and water only when the soil is completely dry. If the plant is non-salvageable, take leaf cuttings from healthiest leaves to propagate.