Ok, I probably wouldn't put it up to an unreasonable level.
However, will definitely add $5/week when possible, to make up for this situation.
The deadlock will probably cost $200 as it's not an easy fit.
If the tenants were nice about it and not so demanding and threatening from the start, my attitude towards them would have been different.
I still wouldn't be installing a deadlock, as I don't like to be pushed by tenants. If it is just because of insurance reasons, check on whether insurance is available without deadbolts.Provide this info to the tenant and also inform them should it proceed to Tribunal you will also be submitting this information. Tell them you have no problem installing the deadbolts, if they wish to negotiate their lease.
You are not being "vindictive" by deciding to increase rent either. You have "improved" the property and need compensation, PLUS you need to increase rent to keep in line with market conditions.