"Absolutely" and "for sure" express agreement. You can say them all by themselves; they don't need to be part of a sentence. In your example, you don't have to think of them as part of the sentence. You can put them anywhere or make them a sentence unto themselves. Absolutely! We're meeting on Monday. We're absolutely meeting on Monday. We're meeting absolutely on Monday. We're meeting on Monday. Absolutely!

I think they both sound great as they are if I heard either spoken that way. absolutely and for sure mean the exact same thing "Guaranteed". The second one sounds best because for sure can go pretty much anywhere, but "absolutely" might go before the word "meeting" more often. All these sounds best We are for sure meeting on Monday We are meeting for sure on Monday We are meeting on Monday for sure We are absolutely meeting on Monday "for sure" is more friendly but it is said so often that it has a nuance of not being always absolutely for sure ;)

The second one is extremely informal, but the word order is quite natural for such informal speech. The first one has an unusual word order and an unusual choice of adverb. I would suggest: We're definitely meeting on Monday.