From personal experience, all that a large variety of plecos(including ancistrus)need to be kept in larger numbers is their regular requirements(driftwood, a few caves, good water conditions, good diet) along with as much territory as possible. Some plecos will go from cave to cave because they like multiple areas, so it is very important to have many available territories to avoid disputes. If you can accomplish this, they may eventually become more comfortable around each other and share territory & eat together as well(this isn't common, but it does happen).
A large amount of territory is especially important if there is a large size difference of your fish. Larger & more mature plecos handle stress and disputes MUCH better than smaller ones.
I recommend a good piece of driftwood for each pleco, and as many caves as possible. Avoid sharp parts of rocks as well. Plecos love areas that they are in a somewhat tight space(at least mine do) so take necessary precautions to avoid possible fin damage. This way, if one has damaged fins, you will for sure know it was another fish and that there is a problem.
Feed in different areas of the tank also, the last thing you want is them fighting over food.