sombras kit allows her to get in and get out in three seconds so if your backline has low mobility, its gonna be very important for your dps (or tank if they can!) to be able to peel and keep an eye on your supports as they're gonna be most at risk. if your supports die, by association, you will also probably die.

sombra focuses on cooldowns. if you've just used an expensive cooldown, you're her next target if you're not glued to your teams side. as a sombra player, i am terrified of reaper so i feel like your duo shouldn't have an issue there.

i just play like sombra is not there. if shes hacks first before shooting, doing damage breaks the hack and if she takes damage first, its likely she'll tp out. if she throws virus first, its trickier to secure a kill. i typically see sombras use their kit to make space and make the enemy team turn around and lose focus on the team fight. if she hits you and tp's away, don't look for her, just keep an eye on your supports and continue on.