Unvented WM drain, and wants to add a sink in basement

A friend wants to add a sink in the basement to wash the dogs. The only thing in the basement now is the washing machine, which has a short stand pipe, and no vent. The pipe (a 2") runs with slope straight along the wall to the main drain line for the row of townhouses. It does have a trap, but no vent. It runs probably about 12', then once above the pipe, turns down about a foot before it goes into the 5" CI drain with a WYE.

What I was thinking was to cut off the existing trap, put in a WYE to a new trap and standpipe for the WM, and extend the line to where the sink will go and do the same. Planning to add an AAV at the sink to keep the WM from sucking the drain dry, but not sure where to put the fitting to run up to the AAV. Was thinking about putting a cleanout at the end of the second WYE for the new sink.

Should we put in two AAV's, one for each fixture? Where to tap them in? Is this likely to work? The WM connection has worked for 25-years. The sink won't be used very often, and will likely end up fairly high so they don't have to bend over very far to wash the dogs, and to have enough height to use a gravity drain for it.

The washer may be draining, but it may also be siphoning the trap.

You can vent each fixture, the washer and the sink, bring the vents together and use a single AAV

That makes sense. Considering the pipe runs nearly horizontal along the wall, what would be the best fitting to run out into the room to attach the trap and to get a takeoff to insert the line to the AAV? A WYE to bring it away from the wall, with a SANTEE for the vent line above, then the trap?