Font different in IOS vs Windows

Site URL: https://grouper-star-jej6.squarespace.com/

Hello, 

My web designer has used custom code (Will Myer's) to get the look our company wants for the site. However, we are finding discrepancies in font styles and size between Macs vs. PCs, Android devices vs. IOS, Ipad vs phone, etc. 

Basically, we want a consistent font height and look across all media. Does anyone know what's wrong? 

The site is: https://grouper-star-jej6.squarespace.com/ 

PW: 123

The below images show the discrepancy between font sizes. The secondary navigation bar should have the same font size as the project titles, but this is not the case with the Windows version. 

Thanks for all your help!

try adding to Home > Design > Custom CSS

div#block-b151fd50c75e505bbaa1 * {
    font-size: 24px !important;
}

Thanks tuanphan, 

Also, do you have any idea about the font? I used a custom font - Futura Book. 

It is not showing up properly on IOS devices.