Between 8-10 months dogs go through a chewing stage that can be more intense than earlier chewing phases. It has nothing to do with teething and everything to do with teenage energy.
The importance of crate training is very apparent at this time. It keeps your stuff safe and keeps them safe. You do not want to come home to a shredded couch or a sick dog.
If you can secure a safe area for them to be then thats fine, but even a bathroom or kitchen has tons of hazards which bored mastiffs can tear up. It can also be a mistake to confine 2 large teenagers together in a small space. If they decide to challenge each other (which teenagers can do) there is no escape for the underdog.
These are youngsters with energy, not yet the mature lazy dogs they could
become. They need energetic outlets and rest. So if the time you have together is well spent then the down time is okay.
If you can do doggie daycare for one or both that would be great. Even 1/2 a day at a time is huge, and it is also a good idea to separate them a fair amount. You don't want them to be overly bonded to each other. Different days at daycare or separating them in crates can help with this.
These pups are not house trained. If they are soiling the house they are not house trained. Holding 'it' through the night doesn't mean a lot. The bio-rhythyms of the night are different, the body shuts down as we rest and sleep deeply. But during the day with activity we need to go more often. If they are forced to soil inside because no one is present to let them out, then we have left them for too long and/or not taken the time to teach them to hold themselves.
You have taken on a big challenge with these two gorgeous animals, and it requires a higher level of management and training. Thanks for bringing them home, but it will come down to good training to determine if this was a good choice for all concerned.
Love Them & Lead Them,
~Elizabeth & Doug
Dog Training the Way Nature Intended