Welcome to the forum and soon to Switzerland.
If your contract is for a year or less then you'll get an L permit - so that's what you'd put on the form. If you contract is for over a year/indefinite then it would be a B permit. It would have no number because it hasn't been issued to you yet.
No, you can't use your Irish address. I assume you have some sort of accommodation already sorted out? If so, put that on the form - it would ideally need to be an hotel, temporary flat/house you're staying in for several weeks so the permits can be sent to you when they're ready. If you don't have any of this then I'm not sure you can apply for the visas for them to be able to travel with you. One of the requirements for family reunification is that where you're living is big enough by Swiss standards for all your dependents.
https://www.ch.ch/en/family-reunification-eu-efta