"Draw both houses, please."
Translation:Нарисуй, пожалуйста, оба дома.
An interesting observation. AFAIK there is no such connection, but I cannot imagine a sentence with "пожалуйста" and an imperfective verb.
Though... If it's about a continuous action...
- Ты лей, пожалуйста, воду, а я буду мыть руки.
or offering (permission)
- Пожалуйста, ешь сколько хочешь.
Yes it is. For 1, 21, 101 or any number ending with "one" (that is, eleven not included) it is just the singular form. For 2-4 and numbers ending with those (again, "teens" not included) "дома" will be used. For 5-20 and all other numbers "домов" will be used (imagine thinking that more than four is just a lot of). "Оба" in this regard is treated just like "два".
By the way, historically this "genitive singular" for 2,3,4 was neither genitive nor singular - but "dual", a special form for two things instead of singular and plural! So no need to look for possession here (not 2,3,4 things of something). It has just acquired the same ending -a as genitive singular (or as accusative singular for animate males). I'm no expert, just found it sort of a "fun fact" :-)