I wouldn't trust any of the wearable mating protection products, particularly as your only form of protection. Both because dogs are super creative and persistent about getting around these things, and because they won't stop the male from pestering the female and could increase the chances of scuffles. Female dogs in heat can be extra sensitive and irritable, so even if she's usually really tolerant, it's not worth the risk. The best setup would be keeping two barriers between them at all times (ie a crate and a closed door, two closed doors, a fence and a leash, etc.), with the understanding that they might test barriers that they never have before (such as jumping a baby gate that they usually respect). Or, as Lillith said, sending the male on a "vacation" with a friend or family member for a couple weeks.
The good thing is, unlike humans, female dogs can only get pregnant in the fertile window during their heat cycle, which for most adult females only happens twice a year (might be less for juvenile dogs). Read up on the signs and stages of heat (also called estrus), so you'll be able to recognize when she's approaching that window and know when to implement your extra precautions. And, of course, remember that any other males in the area will be extra keen during that time as well, so avoid situations where your female is, for example, unattended in your yard.
It's also a good idea, with two puppies so close in age, to make sure they're getting time apart - separate walks, separate training sessions, etc. This will prevent them from being so tightly bonded that being separated during her heat cycle is super distressing to both of them. Essentially, dogs raised together from a young age can develop separation anxiety from each other (and other behavior issues) if they never get used to being apart. This is called "littermate syndrome", if you want to read up more about it, and it can happen even in dogs that aren't genetically related. It doesn't always happen, but it's good to be aware of!