How to spice up our sex life as we are too tired and busy with everything? Hope it doesn't affect us in the long run

Agree, get someone you trust to watch the kids, put on some clean nice clothes, go out for dinner and check in to a hotel for a staycation. Alternatively, you can skip the dinner bit and just order room service ;)

Sounds Super Duper unromantic, but you just gotta plan time to get the deed done. Hire a babysitter, get a wax, mani-padi done, hire a masseuse home (lots available on gumtree) and spend some time loving :)