How do I use several internet lines and disburse them throughout an area?

Be very careful there is really no way for you by your self to combine multiple connection into a larger one. You can send say traffic from user 1 to connection 1 and user 2 to connection 2 but it not possible for user1 to use connection 1 and connection 2 at the same time to increase a single session. This is the key difference between load balancing and link aggregation when talking internet connections. Load balancing assume you have multiple users and sessions that it can split. There are huge issue because the different connection have different IP addresses.

Since you are talking to the ISP anyway and you are going to purchase multiple connection from them they may be more responsive to other solutions. It is technically possible to place a device on each end of the connection that will combine multiple circuits together. Since this is done at a lower level than IP addresses and you have equipment on both ends it is possible to really combine the lines and get a larger circuit.

What exact device would require more details of how the internet connection are delivered since various dsl versions are different. Still even if they did not want to use the specialized equipment it is possible to do this a couple different ways using commercial routers. If all else fails a load balance by packet with a routing protocol on any commercial router will do the job.

The key here is a having a device on both ends of the connection. Without one at the ISP side it is almost impossible to do this. If your ISP has any clue they will have a method they prefer to do this. It should not be real expensive since it is a one time cost for the hardware and maybe a tiny amount of electricity and rack space on their end.

Eww I got bad news for you. You can't normally just order multiple 'DSL/Cable' lines then redistribute them in a apartment complex, as that violates the agreement between your business and the contract terms of the ISP (your now competing with them as a ISP provider). The 'Norm' is you contact the Business Division of the ISP provider, and they can provide several options from, they do all the work and techie stuff to just providing enough bandwidth to the Point Of Entry (the box that is their equipment).

Now that LEGAL LIABILITY is out of the way (to avoid loss of service, breach of contract lawsuit and repayment for services multiplied x number of units your providing to = LARGE lawsuit) consideration, you have a choice on how you do this. The first is everyone (like with telephone or cableTV service) gets their own 'run' and are liable for the service themselves. So the ISP comes in and wires to each apartment on their own and they are completely having to deal with the issues of the service then you. Some apartments you can't do that and they have (as I said before the Business Division) special 'team' setup due to the design of the apartments for a pre-made alternative solution.

Second is similair to what you have now, you order a high speed connection, as you want multiple units to have HIGH speed (each about 10Mb or more ) connectivity, then you would look at this like office building and would have to spend some serious capital for the service and having a 'support line' to contact like a business has a IT Department to handle such things. Some local IT companies provide this service for you on a contractual basis, and will do this leg work as well, so not to make you turn away from your primary business (Apartment rentals) and be so focused on being a IT provider.

Again the ISP Business Division would need to be contacted to get access to this level of Internet. As your talking 80 Apartments each with say 10Mb or more speed your talking 800Mbs or more (1Gb) of speed you want dedicated to the 'building' to then be split through the router the apartments connect to. This would be OC-24 1.244 Gbps which is very costly on a per month basis (again you can contact your local ISP Divisions and see how this pans out in your area, some have special deals due to location near FDDI rings, and so forth).

That addresses how to get 'speed' to the infrastructure and whom will be responsible for it. Now the issue comes down to Management of that responsibility. The stability would often probably be someone is hogging connections downloading stuff or for example only 4 or 5 tenants watching Netflix causing everyone to suffer. You would need to install a professional Switch and Router, with a network management console (usually built in to the CISCO equipment) that would put 'bandwidth caps' on each drop/port to ensure stable connectivity for all (i.e. no one person is hogging it for everyone). This also would need (for legality CYA purposes) notification of a policy change and how specifically this will affect each apartment and why (your limiting their Internet speed and probably going to increase their rent to defray the costs of all this with additional fee).

The last alternative would be to not only get a proper 'pipe' to the building to sustain the amount of users (consider the average home has 2 computers, at least 2 phones which get on the Internet, a Blu Ray (Internet), then start to add the iPads, Xboxes and PS3s and you can see ONE apartment can have half dozen or more 'connections' normally) but require all places utilize Wireless instead of wired connections. This makes it even easier as you don't need to worry about compromising the infrastructure (drilling new wiring panels and ports, etc.) and you can monitor and record activity to legally protect your business from illicit usage (i.e. someone downloading childporn and they trace it back to YOUR company and raid YOU in the middle of the night to capture the potential child molester at home). Further if you see a particular apartment / devices connecting hogging it for everyone, you can use that evidence when they sue you for defamation and racial bias, you again protect yourself by showing the records of how much use they were using and THAT is why you limited their use, not because they are XYZ.

In all these cases, as you can see, your spending ALOT of time away from your main business model and instead getting into all about IT and how it works, and how to manage it blah blah. My main and final solution; HIRE A BUSINESS SYSTEMS ANALYSIS to come in and do a assessment of the IT needs, demands, options, and opportunities. They would be empowered on your behalf to limited negotiate but not sign contractual obligation without your final approval with all necessary entities to do a study, draw up plans, and then provide you a series of options. It would be best to have some ideas (hence why I provided what I did) on the costs expectations (be realistic) increases, the current costs, and how to best defray over the long term the additional costs in your business portfolio.